I would not risk lowering it well under the soil as sometimes it can cause rot. You could put rocks over it. Just let the offset grow a bit longer then remove it and root it down.
There are several ways of rooting cuttings. The plant in this first video was not producing offsets because it was rotting, since it would have rotted long before it could produce those offsets. The brownish bottom part was just old growth, not rot. As said in the video let the cut surfaces callous over for a few days before planting. Unlike "normal" plants cacti do not immediately need water or planting and can lay around unplanted, or dry root, for a week or two without harm, yet watering too soon can rot them. :-
https://www.youtube.com/watch?v=PMpJ1V2oYUM
This one does not use soil at all. If the cutting is thinner than the glass container just wrap in paper kitchen towel or similar to hold it up off the bottom of the glass:-
https://www.youtube.com/watch?v=WesnP1ZW1c4
With the mention of rotting plants, and it happens to us all at times no matter how long you have been growing them, it may be helpful to deal with it
here for beginners. Occasionally the rotten part will seal itself off and can be peeled off, but usually it has to be cut away to save the plant.
It is important to remove all traces of the yellowish or brownish rotting tissue, particularly in the central vascular bundles or it will simply keep rotting. You need to cut back to healthy tissue, let it callous over as with a cutting, which it now is, and re-root it as with cuttings above:-
https://www.youtube.com/watch?v=vb8W2PqBSYU
I have usually used flowers of sulphur rather than corn starch to dry the cut, but whatever works for you.
