To find the office-
when you will be inside the HQ then look around you see a way in the right side of the screen then go there and you will see a board saying 'training' just
go near the board and look around and you will see your checkpoint

To find chief's office-
when the cutscenes will be over then just walk back and look around and you will see staires going up then go up there and you will see a board saying 'administration' and pointing 
at left then go to the left side and you will see a big office straight ahead just walk near the office and you will see your checkpoint

Sorry for my bad ENGLISH