In order to find your User ID/Shortcode you need to have Editor’s rights.
Editors can access an ID for each user by going to SWITCH TO ADMIN section in the left-hand navigation panel.
Select the [Client name] > Manage all users.
Click on More … menu. The user’s shortcode is listed here.
If you are Content Publisher or Content Sharer and don’t see this option, please contact the person who has been assigned the Editor role.