The short version is that you don’t, without physically moving the limit switches, but it doesn’t actually matter. You can place the user origin anywhere you like, and it’s remembered until you change it.
LightBurn will also send work to exact place on the laser that you have placed it in the workspace if you’re using Absolute Coords mode.
You’re likely used to GCode systems or CNCs. DSPs have a few differences to get used to.
In LightBurn, you simply tell it where the origin point of your machine is, and artwork will be oriented correctly when imported.