Make sure that:
Importing an arena/map into SkywarsReloaded is a bit tricky as there is no command or something like that to do it for you.
There are two ways to do this, with WorldEdit or by coping the world.
If you have a small world, it's recommended to use WorldEdit, as copying the world is a bit more work. Make sure to not copy big worlds using WorldEdit as it may crash your server.
All following steps contain two ways, WorldEdit and WorldFile. Follow your preferred way.
Let's start with copying the arena. You can do this by setting the 1st and 2nd position with either the wand or by using //pos1 and //pos2. Set pos1 in the left-bottom corner of the arena, and pos2 in the right-upper corner. Then type //copy.
Go to the world folder. Then copy all files INSIDE the world folder (data, region, level.dat, uid.dat). Now remove the world folder.
Now remove the world (do NOT restart the server as you will lose your WorldEdit clipboard then!). Then create a new map using /swm create [map]. If you don't know how to do this yet, take a look here here.
Create a new map using /swm create [map]. If you don't know how to do this yet, take a look here here. Don't do anything about the map (except setting the meta settings) and just save it.
Paste your clipboard using //paste. Not just save your map, add the player spawns etc. and register the map. You're done now.
You're not done yet when following the world folder course. You've now saved your map and the world is still empty. Now go to the folder of the NEW skywars map and paste all copied files into the folder.
Now restart your server. Use /swm edit [map] to check if the world transfer has succeeded. Don't forget to set all arena settings.
Now you HAVE to perform /swm save to save the changed world into the skywars system. Otherwise, the world will be reset when the game ends, because the Skywars system hasn't got the changed yet. If you want the map to be playable, don't forget to register it.