Excuse me for this shabby guide but I hope it helps you to allow your gamepad/joystick/controller ETC. Work in the sim.
This guide will be updated and comment below if anything changes or any troubles occur and I will try my best to help you resolve it.

The Program we are going to use is
TocaEdit Xbox 360 Controller Emulator 3.2.9.81 for 64bit games
This is an Xbox 360 controller emulator which will allow you to change any inputs into Xbox 360 gamepad inputs (As long as it recoignises the gamepad so Have your drivers up to date)
Download https://www.x360ce.com/

1. After downloading the file it will be in a .rar file so make sure you have some program to extract that.
   
2. Next you want to extract the files inside the .rar file into the game folder itself (This can be found under \Steam\steamapps\common\FPV Drone Simulator). This should leave you with the file x360ce_x64.exe inside your game directory.

INSTALATION COMPLETE

This part will be different for every controller so I will be explaining the program as best I can

1. Run the Excutable
   
2. Press create
   
3. Press next
   
4. Press Finish
   
5. Close program
   
6. Rename xinput1_3.dll to xinput1_4.dll this is the name of the config the simulator uses and looks to find, without changing this it will not work (Does not change for controller, this file name should work for all)
   
7. Reopen the Executable

Next you only really have to configure 2 of these pages (Not too much in each page)
These are the pages you need to configure

1. General
   
2. Advanced

First lets start with advanced
The only thing we need to change here is the Device Sub Type to match our input device, For E.G. Im using a flight stick so I chose flight stick

Next we need to sort out the Axis
to do this go onto the general page and this chart provided in the simulator will help you chose what axis needs to go where
How do you find which axis you need to use?
Mostly trouble shooting
my throttle is my Z axis so I need to find out what Z axis is in the executable (as the executable names the axis Axis 1,2,3,4.... ETC.)

After going through all of this I found these axis to work with a T.Flight HOTAS X
Once you have your axis set and buttons configured press save
Close the program and open the game, enjoy :)
(Showing where the axis are found and what axis work for my T.Flight HOTAS X on the last Picture)