Hey!
I believe that the plugin you installed is Multiverse, if so, then the /spawn is not related to Multiverse at all. If you are using essentials for /spawn, then you can only use it for one world only. If you want to add more spawns, then you should make warps (/createwarp). If you want it to be any other command then /warp, then you should use the plugin Skript for it, although you have to code it yourself.