One thing you have to get used to is that servos can't be controlled directly with pushbuttons or momentary switches at all. They need (at minimum) a circuit that produces the right electronic signal, and maintains it continuously. It's possible to do that with an oscillator circuit like this:
Although that one is set up with a control knob for sending the servo to any position, it would be easy to use a toggle switch instead, and just have two positions.
If you want pushbuttons or DCC for input, then you have to use a microprocessor circuit like Tam Valley makes.
"Against dirty track, the Gods themselves contend in vain."