klick orange download button under "Files"

• double click on the .scad file to open it in the editor

• select all

• copy it

• go to https://openscad.cloud/openscad/

• paste copied data of the .scad file into the editor (right of the 1 in the picture)

• set the variables to the specific value you like

sometimes I add comments like "//[Yes,No]" which give you the availlable options

• If something went wrong please close the tab and open it again. Paste then the code again.

Klick the marked "Export STL" button to export your customized file. 

Then you can print it :)