I just realized that I didn't enter some information that was needed in my tax filings before filing. Now I need to fix those errors

[Critter-3]

You cannot change or add anything on the return that you have already  e-filed.  It is too late, just like when you put an envelope in a US mailbox it cannot be taken back. 

Now you have to wait until the IRS either rejects or accepts your return. Which won't be until Feb 12 this year. If your return is rejected, you will be able to go into your account and add or change it and resend it.

If the IRS accepts your return, then you have to wait until it has been fully processed and you have received your refund or paid the tax due. THEN you can prepare an amended tax return 1040X  but in the meanwhile, DO NOT change anything on your return until you start the amended return. If you did change or add the missing info then take it out and put your return back to the way it was when you first filed it.

You can check your efiling status here,
https://turbotax.intuit.com/tax-tools/efile-status-lookup/

How to amend an Online return
https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-turbotax-online-return/00/27577