X-axis endstops lowrider

So the x axis only has one mechanical endstop.
This is obviously for homing the x axis.
How do I set the maximum x axis now? I’m assuming using a soft endstop. Is this embedded into the firmware so it doesn’t matter what software I use (octoprint/cncjs) or if I reboot/turn off controller is it stored permanently.
if it is embedded in firmware, how do I set the maximum x axis endstop.
I’m new to this so a detail step guide would be ideal.

I posted the answer on how to modify Marlin in your previous topic. I haven’t built a Lowrider, but I would generate the X and Y size by testing the machine, not by using the workspace entered in the calculator. For example, I know on the Primo that stop block placements impact X and Y working size.