Redheather:
The tax data file ends in *.taxYYYY so for a 2018 return, if you want the data file, search your computer for any file ending in *.tax2018 file extension. That's the most important file to keep since you can open it in the software. If you also made a PDF of the return, you can search for that as well.
If you have a Windows PC with multiple user accounts, search from within each account, and also in the Recycle Bin.
See VolvoGirl's more detailed answer below.
