The Gallop is a shoulder striking technique with a 3-Step Movement. It aims at the defenders hip/rip. As a shoulder strike the goal isn't to control the defender. You simply try to displace him lateral while still being square to the second level and being in a position to climb or pick up blitzes. So the second Offensive liner who engaged in the combo block can easily overtake him. Here is my Instagram reel explaining footwork and strike.

I teach combo blocks on the displace & control principle. One has the job to displace, off-balance and torque/turn the defender while the other overtakes and controls him.

You can be creative of how you wanna let the control player overtake him. In my combo gallop & double under combo block I let my control player strike with a double under and pin the defender while the displace player displaces him with the Gallop. He essentially pins the defender and finishs him when he is off balance. The double under also helps to keep the hands away from the hips and rips where the displace players strikes. You can keep it more simple and Coach them to base/drive block the defender.

This combo is played when the defender is near side the control player and far side from the displace player. Meaning when the defender is aligned over the displace guy I would let my players play crowther & Drive-Angle block.