Hello, somehow i've created two turbo intuit accounts. how can merge both accounts?

Sorry--TurboTax accounts cannot be merged.  Pick one and stay with it going forward.   Keep a record of how to get into the "old" one just in case.

...and if the account, not expected to be used going forward, has any older already-filed tax returns in it....then download the PDFs for them now, and back up to a USB flash memory stick.  TTX removes one year's PDF files as each year progresses... so that right now, only the years back to 2017 or 2018 are available as PDF files anymore, and nothing before then.