How to cross-post?

I’m a long time Reddit lurker who’s learning how to post for once. Sorry if this has already been asked but I can’t find a thread about this. How do you cross-post? I’m posting in https://sh.itjust.works/c/velvethippos and want to cross-post in https://lemmy.ml/c/aww and https://beehaw.org/c/animals. Any help is appreciated!