Hi @sakigokmen,
It seems that you have the “second screen only” set as desktop mode.
You can easily attach your main display by switching to extension/duplication mode.
Just open the display settings window, in the multiple display dropdown menu, just select “Extend..” or “Duplicate..” OR via display switch, just press Windows logo key + P hotkey then select Extend or Duplicate.
For assistance, please check Configuration and Settings -> Windows Driver (Primary Machine) chapter in the user manual https://forum.spacedesk.netuser-manual/.