Honestly, I don’t have much experience in this department, since I don’t have much to be jealous of, but I think that just from my experience as a human being, you should try to talk to them. As in, try to understand what they’re jealous of. Then maybe you can help them get it. If it’s not that simple, maybe try to show that it’s not really all that great, so they shouldn’t be jealous (I don’t know if the way I explained that made sense). If that doesn’t help, and they’re just toxic, then maybe don’t be their friend anymore.