How can I re-do my federal return and start over. I forgot to add a lot of things. House interest and 401K.

First----we need to know if you already e-filed.   If you already e-filed and the return was accepted, then you have to wait for the IRS to process your return and then you can amend it to correct your mistakes and add the missing information.   Do not try to change your return until it has been processed.

If you have not e-filed yet, then you can clear and start over if you have not  registered,paid or filed then you can clear and start over:

CLEAR AND START OVER

https://ttlc.intuit.com/questions/2586254-how-do-i-clear-and-start-over

Did you file it yet?  You only enter the 401K from your W2.  Did you enter your W2?  The 401K won't affect your return.   Or did you take a distribution or rollover your 401K and get a 1099R?  House interest will only affect your return if you itemize deductions.  And most people take the Standard Deduction.  

You probably don't need to start over.  Just add the things you missed.  But If you haven't filed, registered or paid you can try to clear and start over

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-clear-and-start-over-in-turbotax-online/00/26444

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

How to Amend this year

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-federal-tax-return-current-year/L7eS6o1qh_US_en_US