What's not written in God's Word is that it's not possible to get born again during the great tribulation.
Many who are not right with the Lord having previously been walking with Him (backsliders) will not be taken in the rapture and those that don't believe in the rapture will not be taken with so according to their faith it will be done unto them (they reap what they sow)
So right off the bat there will be those that recognize the error of their ways having been left behind and will be repenting and getting right with the Lord having to go thru the great tribulation - and these people will be witnessing to others telling them how to get right with the Lord so there's more believers coming on board there
Those left behind will be killed and it will be too late for them to repent. That is what Jesus taught. Please read this.
Luke 17:26 “Just as it was in the days of Noah, so also will it be in the days of the Son of Man. 27 People were eating, drinking, marrying and being given in marriage up to
the day Noah entered the ark. Then the flood came and destroyed them all. 28 “It was the same in the days of Lot. People were eating and drinking, buying and selling, planting and building. 29 But
the day Lot left Sodom, fire and sulfur rained down from heaven and destroyed them all. 30 “It will be just like this on the day the Son of Man is revealed. 31 On that day no one who is on the housetop, with possessions inside, should go down to get them. Likewise, no one in the field should go back for anything. 32
Remember Lot’s wife! 33 Whoever tries to keep their life will lose it, and whoever loses their life will preserve it. 34 I tell you, on that night two people will be in one bed;
one will be taken and the other left. 35 Two women will be grinding grain together;
one will be taken and the other left.” [36] 37 “Where, Lord?” they asked. He replied, “Where there is a dead body, there the vultures will gather.”
Let's start at the beginning to see what Jesus taught in this passage. First, in verses 26 and 27, He talks about the days leading up to His second coming being similar to the days of Noah that preceded the flood. Then He points out that "the flood came and destroyed them all". All who were left behind outside the ark were destroyed, in other words. Then He points out similar things about the days of Lot in comparison to the days leading up to the second coming of Christ and He again points out that all unbelievers who were not taken out from Sodom like Lot and his family were left behind in the city and were destroyed by fire.
Then Jesus points out that no one should try to save their possessions because it will be too late for anyone to do that and anyone doing that is too attached to the world and their life in this world instead of being focused on eternity and being with Jesus like they should be. Lot's wife is given as an example of how we can't be too attached to this world and our lives in this world. That is unacceptable to God for us to love our lives in this world more than we love Him. Lot's wife paid the price for loving the world and her life in this world more than God and that's a warning for everyone.
Then Jesus, using Lot's wife as an example, said that those who want to keep their life, like Lot's wife did, will lose it (will be killed) and whoever loses their life (is willing to give up their lives for God) will preserve it (will be spared and not killed).
Then we get to verse 34 where Jesus gives examples of two people being together with one being taken and one left. Those verses, in and of themselves, tell us nothing about what happens to those taken and to those left, but we can figure that out from the previous verses that speak of events where some were taken away and escaped God's wrath and some were left behind and did not escape His wrath, like in Noah and Lot's days. From those events, regardless of what it means to be taken and what it means to be left (there is some disagreement about that), we know that it means all people either survive Christ's second coming or they are killed. The ones who are left behind on the earth do not survive to face tribulation as pre-tribs believe. They are killed just as those left behind out of the ark were killed and those left behind in Sodom were killed.
Some people think the question the disciples asked at that point ("Where, Lord?") is related to where those who are taken are taken to, but I disagree with that. I think they are just asking where it will take place that one is taken and one is left and Jesus is saying it will happen wherever a dead body is found. Since His second coming is a global event, His answer to the question is basically "everywhere" since unbelievers all over the world will suffer His wrath and vengeance when He comes (2 Thessalonians 1:7-10, 2 Peter 3:10-12).
So, this passage is a problem for pre-tribs who think those left behind survive to live another day and then have to face "the tribulation". No, they do not. They will be killed, just as Jesus taught.