If you e-filed it you will have to wait for it to be rejected and then you can fix the PIN. The IRS will begin to accept/ reject returns on Jan. 27. Do NOT try to change it before you get the email telling you the return is rejected.
Your return is still in pending on the server because the IRS will not begin to accept/reject/process returns until January 27. Only a few returns were accepted early in a test batch. Everyone else has to wait.
https://www.irs.gov/newsroom/irs-opens-2020-filing-season-for-individual-filers-on-jan-27
So watch your emails and spam folder to make sure you know after Jan. 27 if your return was accepted or rejected.