The chords for "I Am Not Who I Was" by Chance Peña are:

• C (often C with a G in the bass)
• Fmaj7 (F major 7)
• Am (A minor)
• G

Sometimes C9 (C with added 9th) and variations with hammer-ons are used. The strumming pattern mostly starts with a downstroke, and the song uses these chords in progression throughout the verses and choruses.

Here is a simple chord progression outline from the song:

• Verse: C – Fmaj7 – Am – G – Fmaj7
• Chorus: Am – Fmaj7 – C (sometimes with add9) repeating

This pattern repeats with slight variations throughout the song.

This should help to play the song on guitar effectively.