“How can I regrow bone around my teeth?”

That’s a tough one! Once bone around teeth is lost due to periodontal disease, it is difficult to regrow the bone. Periodontists may do laser gum treatments to reduce bacteria in the spaces between the gums and teeth. They might do deep scaling to physically remove plaque and calculus around teeth. They might use an allograft to fill bony defects along with growth factors. Best is to prevent bone loss by flossing twice a day after brushing and of course regular visits to your dentist for cleanings.

Depends on why you lost bone. See your dentist for a proper diagnosis for the bone loss, Sometimes you need a bone graft or other periodontal treatment, guided tissue generation. Sometimes you would need a root canal. The tooth can be cracked, so then you cannot do anything but extract. See your dentist.
Good Luck.

You can't do that. The only way bone can grow is by doing special surgery and only by trained periodontist, that too only in selected cases.

Once you lose bone around a tooth, it usually won't grow back naturally. However, you should visit an oral surgeon or a periodontist and see if it would be possible to place a bone graft.