Entering loan in notes payable not input during setup.

No, QB is double entry accounting

You create the liability account,
if you enter a starting balance when you create the account the offset entry is equity automatically

other wise do a journal entry debit what the loan was for, and credit the liability account

only you and the company can decide what the loan was used for and how to post it now

Remember that "the accounting formula" is:

Assets = Liability + Equity

Since this entity is More in debt than reflected on the books, you Increase the Loan account (credit) and the Debit is Equity as Retained Earnings or Owner Equity or Unrestricted Net Assets or whatever is your "closing equity" account name.

Putting the amount as an Opening Balance just allows your entry to be lazy and not use the Real Equity; it creates an entry in Opening Balance Equity, which you have to Offset, later. OBE should be 0 and never used again, once a file is set up and in use. There really is no reason to enter it, and then Fix it, afterwards. Just make the right entry, yourself, to start with.