When you are in a highly eccentric orbit (meaning the point in the orbit farthest from Earth (apogee) is much higher than the lowest point (perigee)) like this one there are several maneuvers you can do to significantly change your orbit with relatively little energy. The article describes some of the things they are testing.
A small breaking burn at apogee will lower the perigee into the upper atmosphere and they can then do aerobreaking (use atmospheric drag to lose energy) to slow down enough to land.
As an aside, it's sad about KSP2. We need a good, open-source space simulator in the spirit of KSP, which has incredible enthusiasm in the modding community.
By carefully timing boosting burns at different points in the orbit, you can change the orbit to become highly inclined - go prograde at the periapsis, and your raise the apogee.
From the image, I guess they are in a Molniar orbit [1].