I’m in the same situation but mine is out side, not dried out. Bottom is rotting, same as the one i purchased a mI think ago. Help bottom left is soft & dying

The best option may be to graft it. If you have no experience of this, and many people don't (including myself), the next best option may be to cut off the dead root and tissue, let heal and try to reroot. Simply potting it lower down in the pot would not work well if the bottom is dead. The dead part may rot away and infect the healthy part of the plant.

I have a crested Mammillaria which I have had for about 30 years. It grows so much that it pulls itself out of the soil and needs to be cut into pieces. left to heal and the pieces rerooted. I have about a 50% success rate doing this so it is not a certainty that it will reroot. In my case, enough pieces root to continue the plant and sell off the excess. If I could graft successfully, that may be a better option as it would not pull its own roots out as it grew into a ball shape over time.