I realized that I made a transfer from checking to savings in the amount of $8000.00 on 7/1/2020.

It should have been a transfer from checking to another checking account at the same bank that isn't in my Chart of Accounts (previous owner).

I usually enter it as a ACH check.

I am working on the December 2020 bank reconciliation, which I have at 0.00 difference.

If I delete the transfer and re-enter it as a ACH check to the previous owner, am I messing it up?

Do I go into the check register and mark it as cleared? 

Since I have the December 2020 reconciliation still open, will I be able to fix it right there without undoing anything?