Businesses that applied for the ERTC and were deemed eligible for the tax credit ultimately will have to amend business tax returns for the time period in which the tax credit relates to.
Example: Your business was eligible for the ERTC for Q4 2020, and an amended Form 941-X was sent to the IRS to apply for the credit. Once the money is received for the credit that was applied for, the business will be required to amend their 2020 tax return. The reason being that the business' wages expense was reduced for that year due to receiving money back via the ERTC.
The amended business tax return will generate a new K-1 and therefore personal tax returns will need to be amended too for the years in which the credit relates to.