Notice that there is a Next To Do button in the To Do groups section.

This button will select only the records assigned in the T button. The field on its right determines the number of records to select only.

1. Enter the number of contacts to select from all contacts assigned to the To Do group.
   
   Let's say you have 100 contacts assigned and you want only 15 contacts to show/selected. Enter 15.
   
   
2. Then, click the Next To Do button.