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. The IRS does not allow you to take it back.
If you left out a W-2, a 1099G, 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, however, then you have to wait longer until it has been fully processed and you have received your refund. THEN you can prepare an amended tax return and e-file or mail it in. You have to be able to work from that return exactly the way it was when it was e-filed originally. You will need to use a form called a 1040X.
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
If you find you need to amend your return after following the advice of @xmasbaby0, here is how to do it in TurboTax:
You can file an amended return using TurboTax for no additional fee. You will see the option on your Home Page in TurboTax, then under Your tax returns and documents, look for an option to Amend/Change your return. You should wait until you receive your refund or the IRS has processed your return, if you sent a payment, before you amend your tax return.