I received a corrected W-2. On the Addt'l Income form, should I post the "additional amount" (about $4200) or the corrected total income ? I already paid $231 AZ tax

If you already filed and you are now amending the return to enter the corrected W-2 you will enter the corrected box amount where the incorrect amount was listed.  So say box 1 used to be $4000 and the corrected box 1 is $5000 then you will change the $4000 to $5000 ... you do not just enter a new W-2 with $1000 in box 1.