For the benefit of others reading this post, there are two ways. Use whichever you wish.
On the scanner via keypad:
1. Menu>Manage Favorites (Scroll to the FL to which you want to add channel)
2. Review/Edit Sytem (Scroll to the applicable system)
3. Edit Department (Scroll to the applicable department)
4. Edit Channel and Select New Channel. Input the data as needed.
5. Press Menu repeatedly until you are back scanning.
Using Sentinel:
1. Eidt the applicable Favorites List
2. Drill down to the applicable Department
3. Click the Green + system to add new channel
4. Enter the data
5. Save the Favorites List and write to the scanner, clicking the "Erase Favorites Lists on Scanner" box.
Usually I'll do any editing such as changing, adding, deleting channels via Sentinel just to be consistent and avoid losing a channel added via keypad.