Contributing to a 401k for previous years

My employer failed to contribute to my 401k for multiple years.  I had money taken out of my checks in 2024 (so they would match it) to make up for what should have been taken out all along.  I received my W2 with the amounts and corresponding years for those amounts, but there is no way to enter that on my tax form.  How can I specify the amounts are for different years?