Who does their payroll? That's who you should pass this over to.

Established by the CARES Act, the ERC provides a fully refundable tax credit which can be taken against certain employer payroll taxes. The ERC is not an income tax credit; it is a payroll tax credit and is ultimately reflected on Form 941.

What they would have done is, every quarterly, they would compute the credit and retain some of their FICA despot funds against their entitlement. If the employer’s payroll tax deposits are not sufficient to cover the credit, the employer may get an advance payment from the IRS.

The American Rescue Plan Act of 2021 has expanded the period this credit can be claimed through the end of 2021. The dates are hit and miss, and the qualifications are a bit of a matrix.

https://www.irs.gov/newsroom/covid-19-related-employee-retention-credits-general-information-faqs

After the fact, there is the ability to file for refunds and then amend the business income tax return. There are service providers that are charging for this service, but anyone already running payroll for a company should have been up on it all along as it developed and changed over the covid years.