SimpleRockets 2 already has a Thrust Vectoring System between rocket engine gimbals and autopilot.
If you just want to have more extreme vectoring you can use XML to increase gimbal range
If you want to vector using inputs other than pitch/yaw I believe you can use input controllers to change what is mapped to the pitch and yaw input ids.
If you want to vector ungimbaled engine (jet or solid or ion), then you have to build it out of a clever combination of hinges, rotators, and pistons.
If for some reason the autopilot doesn't meet your requirements for adjusting the vectoring to maintain a heading/pitch, then you'll have to implement your own PID controller in Vizzy.
-1 Question Too Broad 🤣