In order to add or remove agent(s) to the queue, please follow the steps below:
1. Click on "
Settings" and the on "
Queues":

2. Click the
on the right of the Queue you want to add or remove the agents to from:

3. In the new window that pops up head over to the Agents tab and simply drag the agent from the left column (All extensions) to the right one (Chosen extensions) or drag them from the right tab (Chosen extensions)
to the left one (All extensions) to remove them, after which click Save: