I have looked around the forums and I have not found any way to change settings from in game, for example changing graphics or sensitivity.
You will have to code that behaviour in relation to your game, since changing graphics quality can mean different things for different games. Eg turn on and off real time shadows or post effects.
For the actual menu here is a good starting point: User Interface - Buttons | Learn PlayCanvas
How would I code the behavior in, and would it go across all scenes?