1. Turn off your server
2. Go to file management
3. Click on the file named "server properties"
4. once you're inside the file, look for a line that says "enable-command-block"
5. change this value to either true or false to enable or disable command blocks
6. once you changed the value to either true or false, press the save file button
7. once you saved the file, you can now turn on your server again and commandblocks will be either disabled or enabled depending on what you changed the value to