@ConvoyPerson
Well you'll need to use variables, it should be fairly simple. Change the button input to InvertRight and InvertLeft respectively through xml, go to the variables menu and add these variables and in the input section add yaw or roll or what ever your using to turn. You can change the InvertRight or InvertLeft to what ever

Because I can only turn right

@jamesPLANESii I'm trying to make a car gui that uses buttons and I'm trying to make it so that when you hold a button in the left, it turns left or something

You can't make a button stand-alone that simply inverts pitch and roll There's no input for that. You'll need to make a code for all your pitch and roll control surfaces/rotators whatever to invert their input of pitch and roll when the button is clicked. Basically it will look like this:
1. Set the button to an activator, or any other random word or togglable input
2. Set the input of your control surfaces or rotators whatever that are controled by pitch and roll to [whatever the button input is] * [Pitch or Roll], example, if you want Activate1 to invert a pitch input you'll have to change the code from Pitch to Activate1 * Pitch
Hopefully that makes sense lol @ConvoyPerson

@jamesPLANESii yes

So like, when you press the button, pitch and roll inverts?