Open the world in Minecraft (Java or Bedrock)
Ensure cheats/commands are enabled for the world
Use the command to give yourself a command block
Java Edition: run `/give @p command_block`
Bedrock Edition: run `/give @p command_block`
If the command block item is not available in your version, use the creative inventory search for “command block”
Place the command block from your inventory or use the give command again if needed