Under "My Team" on the left-side navigation bar, click "Assign Job Slots" which will take you to your Subscriptions page. Click Manage Slot Assigments.
Only unassigned slots can be assigned. To assign credits that are unassigned, click the "+" symbol next to the team member's name and click "Save Changes."
To reassign an assigned job slot, remove it from the team member by clicking the "-" sign next to their name. This will add the slot to the Shared Slot Pool where it can then be reassigned to another team member. Be sure to click "Save Changes" when you're finished!