Who can make a solid out of this surface?

Hi friend, I am trying to open your file, but I can't I am using release 20 V5.

Hi friend, I can open your model in another release, and first I would do, the following:

1.- close the other surface, that you have open, with fill command, and after that I made join (selecting all the elements), and when you have joined all the parts, you can move to solids module, and close surface, and done!! just do it, and let us know if you can, dont worry if you have more questions!!!

I hope my comment had help you.

Have a good day.