To have your new signatures on your users, you have assigned your signature template to groups but now you are looking how to change the group' users?
1️⃣ Access to the Users menu
From the menu Users accessible from the left sidebar, select your users with the checkbox on the left of each row or filter your users with the list buttons on the top.
2️⃣ Grouped actions
Use the grouped actions button to directly change one or more group users.
2️⃣ from the user file
You can also change the user's group directly in their user record.