Thanks! I'm glad you liked it :)
There's no rebindable controls in-game at the moment but: you can rebind your controls in the settings file! Just open the file
%AppData%\Tank Commando 3D\settings.txt in the text editor of your choice, and scroll down to Input.Mappings. Listed under there you should find Crouch bound to "Keyboard.LeftCtrl". To change the binding, change this string to something else, like "Keyboard.C", then save and reload the game.