CAn you file your w2's seperatley? Like, if you already filed one, and forgot about another one, can you go back to file it later?

You will need to file an admended tax return, showing all of your earnings, it is possible of course that you may have to pay back some of your refund you got, or perhaps they will owe you more money,

But you need to refile an admended return.

Fr Chuck has got it right! :-)