Step 1: Find your Save Files
1. Press ⊞ Win + R on your keyboard.
2. Copy/Paste %APPDATA%\..\LocalLow\IronGate\Valheim\worlds_local
3. Navigate to\LocalLow\IronGate\Valheim\worlds_local (also check worlds folder)
4. Find the .db and .fwl file with your worldname.
Step 2: Upload your Save Files to the Server
1. Open the File Manager.
2. Navigate to /.config/unity3d/IronGate/Valheim/worlds_local/
3. Put both the .db and .fwl files in this folder.
4. In the game settings, set the World Seed and Game Name to match the name of the .fwl and .db files. In this case, I will set them to testworld.
5. Save and restart your server and the save will be loaded onto the server.