Mistakes happen. What if you receive a refund from the IRS that you’re not entitled to? Or what if you receive one that’s more than you’re entitled to? How you must handle it depends on the details. A paper check refund should be voided and returned within 21 days of receipt to the address in the link below. But suppose you cashed the check. In that case, submit a personal check within 21 days to that address.
If the refund was by direct deposit, contact your bank to have them return the deposit. Also contact the IRS at the phone number in the link. Be aware that if the IRS intentionally changed your refund amount from what was on the return you filed, it will mail you a notice of explanation.
You can find more information here: https://www.irs.gov/taxtopics/tc161