I need to add 1099 misc to already submitted taxes.

[xmasbaby0]

That's right.   Wait to see if your return is rejected or accepted and go from there.

[Affordabletaxes2021]

Remember that since it’s considered a medical expense you would claim on Sch A, your deductible medical expenses must exceed 7.5% of total income in order to be able to deduct them. 
In addition you would need to have enough itemized deductions on Sch A to beat the standard deduction.
It may not make a difference on the return.  

[gbookhmer]

I need to add a 1099 to my already accepted return

[VolvoGirl]

You should not amend until the first return has fully processed and you get the first refund or your tax due payment has cleared.  

The 2021 1040X amended return won't be ready until March 17, 2022.  See this list

Federal Individual Forms Availability