I misread the title and thought it said lithops but see now it says lobivia.

I just took a flat piece of plastic/metal (I used a thick plastic plant label) and stuck it between the pup and mother, a knife would probably be better. After I had stuck it between there a couple times to separate as much as I could, I twisted the implement to pop the pup off.

A woman I know has a clump of Lobivia in the ground and she told me if I could get one loose I could have it. I don’t know what type of Lobivia your thinking of separating, but I used one of those wooden paint stirrers. I didnt want to use a knife because I would most likely stab other cactus that were in the clump. The wooden paint stirrer worked fine.