Start by calling TPG.
https://taxpayer.sbtpg.com/
It may take them some time to return the funds to the IRS, and you might be able to get them to release the funds to you. (However, TPG was a target for fraud a few years ago when they were tricked into sending people's refunds to the wrong accounts, and their new security procedures might prevent them from re-sending the money to you.) But I don't think it will hurt to call them first.
