If your pending return is accepted first, then a return filed by any other preparer will be rejected. Or vice-versa. The IRS does not pull returns on a first come first serve basis. You get to e-file one tax return; others will be rejected. If there are mistakes then the return has to be amended after it has been fully processed.
If it rejected then take it elsewhere, or take it elsewhere to be amended after it has been processed if you want to.
Your e-filed 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.