How to keep the motors on

How do i make the motor stay on so when we pick up the cube the motors keep pressure

Keep sending them a control value, you could use a second button to do this.

task main()
{
    while(1) {
      if( vexRT Btn6U ] == 1 ) {
        // close claw
        motor[port2] = 127;
        motor[port3] = 127;
      }
      else
      if( vexRT Btn6D ] == 1 ) {
        // open claw
        motor[port2] = -127;
        motor[port3] = -127;
      }
      else
      if( vexRT Btn5U ] == 1 ) {
        // hold claw
        motor[port2] = 30;
        motor[port3] = 30;
      }
      else {
        motor[port2] = 0;
        motor[port3] = 0;
      }
    wait1Msec(10);
    }
}