We loaned a tech money (cash advance). I forgot to enter the cash advance on his check because it was in the form of a loan on a credit card for a product. I took the two payments out of his check. How, after the fact, do I show the cash advance?

At the time the loan was made, you should have debited a receivable for the employee and credited a payable for the credit card. If you didn't make that entry, what you do now is going to depend on what you did when you deducted it from his check. That had to be have charged somewhere.

I don't understand what you mean by having forgotten to enter the cash advance "on his check" since you are also saying you took the payments back out of his check. You either did or you didn't. When deducted from his check, it would technically come back off a receivable you should have recorded. What did you charge it to?

In order to straighten out an error, we have to know what exactly you did with it to begin with.

(And hopefully you made that deduction after figuring out his taxes.)