May I assume that you have already e-file your return, and forgot to put the apartment number on your return?
You have two choices: (1) Speak to your local mail carrier and see if he/she will put the envelope with your name but no apartment number into your box, or (2) file a Change of address form with the IRS.
However, given that everything is so slow at the IRS right now because of all the closed offices, options #1 is your best bet. Do #2 anyway, so that it will be right for the rest of the year.
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