Only have 2nd gear

I could use a pic of the shifter green circle.
But the second gear only best case scenario I can see is the valve body is experiencing “sticktion”. A fluid/filter change and a bottle of trans medic has helped similar troubles on auto trans of several different makes. When the pan is off, an inspection could show a lot of wear or other problem.
I’m fine if a C-4 specialist comes up with another answer. Until then, this inspection and fluid change is a common step.

if the transmission is stock to the car, then you have the dual range C4. it was designed so that you could start off in first gear as normal, or in second gear in adverse weather conditions, such as snow or other traction limited situations. as i recall the big green dot means you start off in first gear and the smaller one means you start off in second.

now here is where the issue comes in. in 67(?) i think, ford switched to the normal pattern, where you pull the shifter into drive and start off in first gear all the time. however there is on little quirk of automatic transmissions of the three speed variety. if you pull the shifter into second gear, the car will start off in second, and wont shift into third at all.

what may have happened in your case is someone swapped out the early dual range C4 for a later one, and you are starting off in second gear. try pulling the trans into neutral and then down into drive and see what happens. if you have the full range of gears at that point, then problem solved. if not then go with the advice you were given by 7991LXnSHO. if that doesnt work then change the modulator valve, after making sure the one there is connected to the engine vacuum. also note there is an adjustment on some modulator valves. make sure that adjustment is in the middle of its range. you can adjust from there as needed to get the shift quality you are looking for.