I see no responses so maybe this will help. Is it a Ford or Mazda gearbox? If it's a Ford it's not the easiest of things to get to as the access plug doesn't have much clearance. If you can get hold of the build manual it may help. I accessed mine from below. To get to mine the advice was to cut a short straight piece off the right sized Allen key so this could be inserted into the access plug. The other end of the piece goes into an appropriate sized ring ratchet spanner and slowly turned. Mine was a self build in 2012 so I had to fill the gearbox from above and then get up underneath to put the plug in the hole and tighten it up. Fiddly and mostly done by feel.
On my 6 speed I use a cut down allan key.
I've read of someone else who used an allan key offcut and ratchet ring spanner and managed to get it jammed in the chassis, plug still in and ratchet spanner only able to go one way! I expect it was removed by taking the gearbox fixings out and one engine mount fixing and sliding the whole lot over.
I find approaching from the opposite side to the plug helps as your fingers naturally bend towards the plug and make it easier to manipulate it back in with both index fingers.
On 911s its been known for the filler plug to be very tight and round off, usually after the owner has drained the oil :-0
And its really fun to put back in with your hands all oily !
Definitely open spanner to ensure against jamming. Just needs a bit more patience.
If its a Ford box I use a long series allen key with the short end shortened and a length of pipe. I turned a few pitches off the plug thread to minimise the fiddling and give a lead to get it back in. Its messy....wear goggles....make sure no one can hear you... good luck
A 2016 Academy car will have a Mazda gearbox, so the fill hole and drain are on the left hand side (in the passenger footwell). I don't know the quantity because the are all supplied factory filled with the kits. On a Mazda gearbox the gears stick also needs a small quality of oil. My drain is a hex, but the fill is a square drive.
Don't forget to loosen the fill hole first before tackling the drain. You don't want to drain it without being able to fill.
My detailed build blog