You can edit groups that you have set up in the local directory on a Yealink T19P by following these steps.
With the phone displaying the Idle screen, press the Dir soft key
Select the desired group
Press the Option soft key and then select Detail from the displayed list.
Press or to scroll through the group information and then click edit
When you have finished editing the group, press the SAVE soft key or if you want to exit the group menu without saving the changes, press the BACK soft key.