My suggestion of booking the forgiveness of PPP loan is rather simple:

Debit the Loan liability account where the loan was originally posted, and Credit the Retained Earnings. 

This will keep your Balance Sheet in true balance, remove the non-existent now liability, and also would not create the income that should be considered to be non-taxable but which is technically impossible to show this way in the company's books or on Federal Income Tax forms.  

The other possible option could be to credit Shareholder Equity account, but I prefer Retained Earnings.