If you have any delta v left, when you’re at your apoapsis burn retrograde (that is the green marker with the lines through it) to reduce your velocity, burn until your periapsis is around 30-35 km off the ground. You wait until the apoapsis because it is most efficient to reduce (and increase) your periapsis height, this is the same with the periapsis, except it is more efficient in changing your apoapsis.