Login to the Kinetic Panel.
Stop the server.
Open File Manager.
Follow How to use Cycle Map.
At the top of the page, add workshop_(id)
Replace id with the Steam Workshop ID.
Save the file
Start the server.
If you want to change the active map to a modded map in the console on the panel, enter changelevel workshop/(Id)
Replacing the id with that maps id.
Team Fortress 2 guide
How to use Workshop Map to your Team Fortress 2 Server
This guide will cover how to add maps from the workshop to your Team Fortress 2 Server