First off - 70 code is low temp. You need to get the temp up above 140deg (If memory serves) before it will go into a count down and give you the oil level. What I do in our shop is power brake the coach, put it in gear and hold the brake down hard then run the rmp's up to 1200 or so watching the tranny oil temp gauge. Now depending on where the gauge sender is located you may have to get the temp on the gauge up to 200 before the tranny really is up to temp. It will give the 70 code until the computer sees it's set point which I believe is 140 deg. If you get it too hot code 90 will come up. If your above the min temp and below the max then the touchpad will go into a count down usually starting at 7, flashing 7 something like 17 times, then 6 and again flash around 17 times and so forth until it gets to 1 then it will give you the oil level.
When it gets to the oil level it will flash "O" then "L" (for oil level) then depending if its high, low or ok it will flash "L" "O" for low or "H" "I" for high or "O" "K" if it's ok. After it flashes a "lo or hi" it will flash numbers 1-4 only and that number is how much its low or high.
I set the tranny at 1 hi when we do a service, that way when the customer drives away if its checked it should read ok or hi 1.
As for where to fill, if it doesn't have a dip stick up top, then go down below and closest to the engine side of the tranny, look above the pan, like looking down at the tranny if it was sitting on the floor, you'll see where it goes. I can get a picture if you cant find it.