encoder speed

in the autonomous, where do we put the speed in the following segment
LeftFront.rotateFor(-1030, vex::rotationUnits::deg, false);
RightFront.rotateFor(-1030, vex::rotationUnits::deg, false);
LeftBack.rotateFor(-1030, vex::rotationUnits::deg, false);
RightBack.rotateFor(-1030, vex::rotationUnits::deg, false);

we have the velocity set, but we want to slow down the speed for certain comands

There is another rotateFor command that allows you to put in the rotation as well as the value of your velocity, however you could also just set the velocity of a motor again every time you want to change its velocity.

If you want to a have a controlled velocity it is going to look like
RightBack.rotateFor(-1030, rotationUnits::deg, 55 (<<this is the velocity part), velocityUnits::pct, false);