My customer did his tax return as a HoH with two dependents, He has ITIN, dependents SSNs. He should get the refund. He forgot that he must to renew his ITIN.

He got the letter from IRS CP11 because his ITIN expired and IRS disallowed his credits and Recovery Rebate credit for dependents, and due to this letter he owe money. 

What he can to do now?