I deleted a Mass tax return on my desktop turbotax by mistake. I have paid for the Massachusetts tax program. How do I reload it on my computer. Windows 10

You can't delete "just" a state return only. Your tax file is located by default (unless you changed it) in the documents/turbotax directory and has a filename extention of .tax2018. That .tax2018 file contains both your federal return and all state returns. Maybe you deleted a separate PDF file on your computer instead?
But if you deleted the .tax2018 file and it's not in your recycle bin, it's gone permanently and forever. You'll have to complete it again from scratch. You may first want to search your entire hard drive for all files with a .tax2018 filename extension.
Now if you'll look in the documents/turbotax directory you "might" see backup copies of your tax file that will start with a tilde. For example, the filename would be something line ~mytaxfile.tax2018. If you have any of those, remove the tilde from the one with the latest "date last modified" on it.