How do I delete past year's tax information I entered to TT Online? I ended up not using TT these years.

There is a tricky way to clear out transferred info in the Online version.  But doing this will also clear out all your entries.  Go to Tax Tools > Tools > Transfer from your computer > Continue > then Continue without transferring. 

Or you can over in a brand new account so it won't transfer.

I've transferred last years info, just to save time entering my basic info, to my 2018 tax and I've already filed it. So I'd think removing 2017 tax data wouldn't affect the 2018 tax data, would it? My point is that transfer has happened already and I want to remove the 2017 data, because it is wrong. Is there any way?

Not without clearing out all your 2018 entries.  Oh you already filed?  Then do not change it or clear your return.  You have to keep your return the actual way it was filed ebpven if it has wrong 2017 info in it.  Did the wrong 2017 Info affect your 2018 return?  Like any carryovers or Depreciation?

Oh no you can't delete any prior year returns listed in Turbo Tax.

Of course I corrected all wrong data (I hope I didn't miss anything...) in 2018 tax, but the wrong data still exist in the 2017 tax area and is pretty confusing. That is why I'd like to clear the data I entered for the 2017 and other years I didn't use TT.