You cannot change or add anything on the return that you just e-filed, nor can you stop it. It is too late, just like when you put an envelope in a US mailbox on the corner.
If you left out a W-2, or a dependent, or a 1099 etc…DO NOT change your return while it is pending. The changes will go nowhere.
Now you have to wait until the IRS either rejects or accepts your return. If your return is rejected, you will be able to go into your account and make the necessary changes to your tax return and re-submit your return.
If the IRS accepts your return,
Meanwhile, DO NOT go in and start changing anything on your return in the system, or you will make a mess for yourself. Sit tight and wait until you see what the IRS does with the return you just e-filed
You won't be able to amend your 2019 tax return until mid-February, or after you get your refund, whichever comes later.
This is how you do it in Turbo Tax Online:
Keep in mind, the amendment is a separate tax return from your original return. If your original return shows a refund, you will still get that refund.
If your amended return shows a refund too, you will get a second refund.
If your amendment shows that you owe, it is because your original refund was too high and you have to pay back part of it.