Go to sports and select the team you want to add squad members to
Click the blue "Team members" button top right
You will then see all the qualifying members based on sex, age etc.
If members have not updated their profile then they will be listed under supplemental members (click reveal hidden)
Just check the box next to any player you want in the squad, you can add squad nos if you want to
Remember to click on the green button at the bottom right - update members
Hope this helps, let me know if you need more ....