From Minecraft Wiki
Revoke operator status from a player.
- Java Edition
- Pocket Edition
deop <player: target>
- player (PE: player: target)
- Specifies a player to remove from the list of operators. May be either a player name or a target selector, but target selectors will not evaluate; only actual player names will produce a useful result.
- Always succeeds if restrictions are satisfied. If player matches a name on the list of operators, the name is removed from the list and any player by that name no longer has operator status.
- To remove Steve from the list of operators: