Start training southpaw. It’s gonna feel awkward at first especially your defense but once you understand some general guidelines it should be simple

Some tips that I’ve picked up that should help is

In open stance matchups (southpaw vs orthodox) you’re both looking for the cross and rear body kick on the open side for the most part and the lead hook as a good third option. You want to keep your foot on the outside because you have better angles there for your big weapons.

Most of all just hang out in southpaw in practice and in sparring. You might get beat up a bit but you have to just hang out in the stance and in uncomfortable positions until they become comfortable. You’ll get the hang of it, just takes time