Hi how can I change the default space that "Tab" offers?

Unfortunately, you can't change tab size, but it's planned https://github.com/nesbox/TIC-80/issues/1521

ok, thankyou

I know this topic is a couple years old, but here I am trying to figure out how to set the tab width to 2 spaces, and I see that the planned feature linked in this thread has now been implemented, at least according to the GitHub issue.

What is the line that I should add or modify within the config cart to change the number of spaces for a tab character? Or do we still need to modify the tab character as I see here: System Configuration Cartridge · nesbox/TIC-80 Wiki · GitHub

EDIT/UPDATE: You can change the tab size by running the config cart (not editing it; actually run it). 

Esc -> Options -> Editor Options 

I set tab size to 2, tab mode to Spaces.