1 John 1:9
If we confess our sins, He [Jesus] is faithful and just to forgive us our sins, and to cleanse us from ALL unrighteousness.
“Although the adjective ... (‘righteous,’ or ‘just’) can be used of Jesus in Johannine thought (cf. 2:1; also John 5:30), referring to the judgement of Jesus as ‘just’), the subject of the present phrase, ‘he is … faithful and righteous,’ is obviously God (the ‘he’ of vv. 6 and 7).”
(Stephen S. Smalley,
Word Biblical Commentary: 1, 2, 3 John, Vol. 51, p. 32
I agree with what Dr. Smalley says here. John is speaking in this verse about the Father (cf. 1 Timothy 6:16), not about Jesus.
If I were to amplify the passage I would render it something like this:
”If we confess our sins, he (God, the Father, YHWH) is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.”
That is what I - a Jewish monotheist who believes that Jesus of Nazareth is the Messiah, Son of the living God - would tell newbies.