First we can create the changing rooms. To do so you should access System / Facilities / Changing rooms

Then you will see a list of the changing rooms already created (if you have any) and to create a new one you can press

To edit the already created ones press or to delete them press

Fill the details of your changing room and press Update

Once created,  press Edit and you will see the General and Content buttons

In the Content section you can see the lockers that belong to this changing room and you can also create new ones by clicking