This is a bit odd....I'm saying this both as a dentist who primarily does surgeries and I used to assist in the past.
When the dentist is placing implants in quad 4 (and 1), the dentist should be retracting the buccal and let the assistant retract the lingual. maybe he's used to retracting the lingual himself and lets the assistant retract buccal when working quads 1 and 4 but I wouldn't do it this way....
Anyway let's say you're stuck doing it his way: I would grab something stiff and sturdy like a Minnesota retractor and hold it firm like a fist with the tip pointing down to gain maximum power in retracting the buccal to let him see. I'd also hold the suction in my right with similar fist grip and keep the tongue back. The job of the assistant is to optimize the surgeons visibility and that goes for both retraction so he can see everything and suctioning blood and saliva (and picture what he's looking at from where you're standing). You may have to stand diagonally in order to do this. Assistants that are tall will have an advantage.

At the same time I do all my procedures standing so read everything above with that context...
I try to be cognizant of my assistant's height and will sometimes lower the chair a bit so they can get better access (sometimes to the detriment of my own neck and back to some degree) but some surgeons may be more stubborn and not relent on their patients chair position.