You have 2 options
To activate the Discord-Developer-Mode, you must go to your Account-Settings. Then you open the Tab "Appearance". When you scroll down, you see the Section "Advanced". Under the Title is a button. Press the button. When the Button is blue, you successfully activated the Developer-Mode on your Account. If you click on a user, message, channel or guidl, you can copy the ID
Open "https://discordapp.com/developers/applications" Link in your Browser. Open your Bot's Application. Under name is a Section where is s field with "Client ID". This is the ID of your Bot