Prepaid rent still in force $400 but on the trial balance sheet it states prepaid rent 2,700 do I subtract -debit 400 or credit 400

Unearned Revenue is a Liability and liabilities have a normal credit balance. Prepaid Rent is a Current Asset and assets have a normal debit balance. When you decrease a liability you debit the account and when you decrease an asset you credit the account.

You did not give enough informaation in your problem to determine what to do.

From the information provided by you, you have $400 in Prepaid rent and you paid $2,300 in advance for rent. The journal entry to record this is:
Ebit Prepaid Rent for 2,300
Credit Cash for 2,300

You do not do anything with the $400 until you have used the rent.

Obviously you did not read your problem and did not look at all the information provided in the problem!