You can use several methods to change the world on your server and generate a new one in case you need to have modded structures generate or you just want to start a new world.
1. Open the Basic Server Settings
2. Change the Custom Save Name to any other name, this will create a new save.
Note: This will not delete the old world. You can switch back at any time by changing the name back.
3. Save your config and restart the server.
1. Open the File Manager
2. Navigate to /minecraft/
3. Right click and click Delete on your save folder. By default, this is Indifferent_Broccoli_Minecraft_Server
4. Restart the server.