Altering my dependents after filing

you didn't provide enough info.  from the IRS standpoint, it is not who claimed him but who under the tax laws had a right to claim him.  generally, it's the custodial parent unless the custodial parent furnishes the non-custodial parent with a signed form 8332. which the non-custodial parent must include with their tax return. thus that prevents e-filing

anyway here's the bad news.

 the return at this point can't be recalled. the IRS won't open e-filing until 2/12/2021. so you'll have to wait. if your return is rejected you can fix it and resubmit. if it is accepted you'll have to wait until it is fully processed and the file an amended return