Your default Falcon 4 BMS installation folder will be your C disk.
C:\Falcon BMS 4.38

If you cannot find or know your installation folder path you can use the Alternative Launcher to find where you have installed BMS. Simply start your Alternative Launcher and right click the program on the taskbar, then right click the program name from the menu and finally left click Properties. Under General you will find the location of your install.



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Now that you have the installation folder path, in my case E:\Falcon BMS 4.38, you will need to adjust the following command:

"..\Falcon BMS 4.38\Launcher\FalconBMS_Alternative_Launcher.exe" %command%

For most of you this will be:
"C:\Falcon BMS 4.38\Launcher\FalconBMS_Alternative_Launcher.exe" %command%

This will start the Alternative Launcher which will allow you to change theatre or keybinds, you may also use the following command to start the game directly bypassing the launcher.
"..\Falcon BMS 4.38\Bin\x64\Falcon BMS.exe" %command%

Now that you have the command you need to add it to your Falcon 4.0 launch parameters in Steam.

1. Open Steam
   
2. Open your Library
   
3. Find Falcon 4.0
   
4. Right click Falcon 4.0
   
5. Left click Properties
   
6. Under General/Launch Options paste the command with either the Alternative Launcher or Game executable path

To verify everything is working as intended you can check the following after running Falcon 4.0 through Steam.

1. Falcon 4.0 is running
   
2. The game can be stopped
   
3. The Alternative Launcher or Game booted
   
4. Your status states you are playing Falcon 4.0

Finally, not pictured, you can verify your steam hours are going up as you play.

If you have any questions feel free to ask them in this post or your best bet in general for BMS is to make your way onto the Falcon Lounge Discord server.

BMS recently had a major update going from 4.37 to 4.38, when these major updates occur the game will have to be reinstalled and therefore your path for BMS will change. Meaning you will need to update the path in your Falcon 4.0 launch parameters.

A minor update, such as 4.37.0 to 4.37.1, is not the same and does not reinstall your game. Meaning you don't need to update the path in your Falcon 4.0 launch parameters.