Hi-- I started to make an amendment after I filled but never finish. I have come back to do it now, and it looks like my data is "polluted". Any advice?

You need to be more specific than "my data is polluted".

Is TurboTax able to open the file? If not, is there an error message?

If TurboTax can open the file, which data is incorrect? Please be specific.

What year are you amending?  2018 online?  You can delete the amended return and start it over.

You can delete the amended return this way.  Do the steps slowly and carefully.  After you delete it then you need to manually take out the changes you made to put your return back to the original return.

How to delete an Amended return in the Online version

https://ttlc.intuit.com/community/amending/help/how-do-i-cancel-or-undo-an-amended-return-in-turbotax-online/00/26315