...
Shift left-click on the face or use the up arrow next to Faces to select the face. Click Apply.
(Click picture here for larger image)
Go to Step 3: Specify Boundary Types in GAMBIT
...
Shift left-click on the face or use the up arrow next to Faces to select the face. Click Apply.
(Click picture here for larger image)
Go to Step 3: Specify Boundary Types in GAMBIT