In a trial balance sheet dated 12-31 how would I enter an adjusting entry for unbilled fees at $1650.00 If you need more info just let me know.

Unbilled fees is an accrued revenue. An accrual is when the "event" has happened but no money has exchanged hands yet. In the case of accrued revenue, it means that you have already earned that revenue, but no money has exchanged hands and therefore you are still owed.

It is the same entry as when you've earned the revenues and you have billed it. The paperwork for the billing is not relevant - it's still owed to you. And this is an entry you should already know, as long as you don't make it harder because it's a new chapter.

If you've earned fees, what account is that? And if the customers still owes you, what account is that?