Accidentally added a cash payment - will not allow me to remove it

I went to "add payment" to a client's account, as I received a check for partial payment of their full bill.  Without giving me an option to pay via stripe, check, cash, etc or pick the amount I wanted to add, it just said, "paid in full" and credited the account in full as if I got a cash payment for the full amount.  When looking at the community post history, I see posts that say to go to billing in the overview page and delete the payment but the system will not let me do that.  How do I fix this?