How do I go back and change something about my rent if I already almost finished filing my return

Does 'almost finished filing my return' mean that the tax return has been transmitted?

If not, rent paid is generally related to the state tax return.  Select State taxes down the left side of the screen and make the correction.

If your return has been transmitted and rejected by the IRS, you can correct your tax return and re-transmit.

If your return has been transmitted and accepted by the IRS, you will have to amend your Federal 1040 tax return.  However, before amending your tax return, do not enter the return and do not enter the return and make any changes.

Amended tax returns will not be available before February 23. See forms availability here.

If you used TurboTax Online, simply log in to your account and select Amend a return that was filed and accepted.

If you used the CD/download product, sign back into your return and select Amend a filed return. 

You must file a separate Form 1040-X for each tax return you are amending.

See also this TurboTax Help.