I only know how to do it manually by editing the url. Say you want to visit “asklemmy” on lemmy.ml and “asklemmy” on beehaw, but through lemmy.ml. The two URLs for this look like:
lemmy.ml/c/asklemmy lemmy.ml/c/asklemmy@beehaw.org
This may be a bad example because I don’t know if beehaw actually has an asklemmy community.
Windows 11 on my main desktop, Debian + KDE on my garage desktop, and Debian on my home server and cloud server.