Adding an affiliation to an accepted paper I am the corresponding and the first author of a paper which has been accepted for publication in a journal published by Springer.

I have an important question that is I would like to know whether I can add another university as my second affiliation (before, I only use one affiliation for me) and what should I do to make this addition.

Thank you very much for your time and consideration.
Yes, you can make this change. The easiest way to do it is to wait for the journal office to send you the proofs. If you're worried this might be too late, you can also contact the journal office directly.

Don't email the editorial board because their role is over (they handle peer review, and this is not a peer review issue).