Open your world in Minecraft
Pause the game
Select Open to LAN
Turn Allow Cheats to On
Click Start LAN World
Use cheat commands in chat
For a new world
Go to Create New World
Select More World Options
Turn Allow Cheats to On
Create the world
For Bedrock Edition
Open world settings
Turn Activate Cheats to On
Save the settings
For Java Edition servers
Set allow-cheats to true in the server settings or use operator permissions
Restart the server