I don't see how a president can simply declare $300 Billion in loan forgiveness without Congress approval.

ALL taxes or budget bills have to originate in the House and be approved by the Senate before being signed by the president (the nut sack). That is according to the constitution of the U.S.A.

Debt forgiveness is a change in the budget, and loading the extra debt onto every American is a form of tax. That's not something a president can do by pen or phone. It has to go through Congress.