If the receiver portion of the original controller is still working, then after you verify all the signals and power supply voltages between it and the rest of the controller, noting them all down, you can disconnect just that part of the board from the rest of it (if you don't care about destroying the original controller), then power it from whatever's needed so it will operate. Once it's operating, then knowing what kind of signal it outputs for each remote signal, you can use an MCU (arduino, etc) to translate that to whatever your new controller accepts.
Or do as RunForTheHills suggests and use a new module with that chip on it. (but you still should test what the original outputs for varous remote signals being received).
If there's a spec sheet for the chip (or the adapter boards with it installed) then that will tell you what pins do what, and what kinds of signals it can output.
To test the one you have, you need to trace which pins on the chip are actually connected to anything outside the area dedicated to the reciever. Then measure voltages on all those connections, with the controller just sitting there powered on, and with the remote being used in all of it's possible ways. If you have an oscilloscope you can also verify if the control outputs of the chip are using a digital signal to teh controller's MCU to operate the motor; otherwise you'll have to just note down what voltages you see at various throttle positions, and if you have a frequency counter in the multimeter, use that to see if it detects anything (if it doesn't, it's just analog voltage like a normal throttle, if it does, it's a digital signal of some type, and knowing what that is can help decode it).
If not, and if you know what signal is output by the remote, on what frequency, you can design and build a receiver for it, and then have that receiver translate the signal instead.
Or you could gut the throttle remote, take a pair of something like the ESP32 in one of it's many versions, which have BT, wifi, etc all built in, and use one to read your trigger/buttons/etc on the throttle remote, and have the other one receive that signal and translate it to whatever your new controller accepts.