How to become an operator - xXTurnerLP/mc-server-manager GitHub Wiki

To become an operator you need to have higher privilages, thus you need the server console or someone else who is operator.

If you have access to the server console just type in it op <YourName> where as you replace it with your ingame name. Example: op xXTurnerLP

The same is true if someone else is operator, they can use the same command.

(Note: Remote Console (rcon) Protocol can be used too!)