Hello, I have a client who contributed the max to a solo 401k for 2024. I filed for an extension while the client was waiting for some additional documents. The documents changed the max allowable to contribute to the 401k, however the client already made the contribution thinking it had to be done by 4/15. We are now past 4/15 - can the client simply withdraw the excess given the extension? He was advised by the brokerage bank to file form 5330, which reading briefly seems to be for a refund of excise tax. Any guidance which schedule should I complete?

Thank you!