How do I fix a herniated disc?

Time, PT, surgery. Most herniated discs do not need to be fixed. They are not symptomatic and the body will adapt to them. If there is a symptomatic herniated disc, it will likely heal on its own. If persistent, mckensie pt can help. In rare cases of persistent leg pain with a herniated disc, surgery is the best way to remove the offending fragment.
Fix, Unlikely... Core strengthening can be the source to heal the disc as best as it can. Sometimes epidural injections are needed to reduce to the pain to keep with the exercise routine. Finally a fix would truly be surgery, in which you cut out the offending part of the disc, however it has its risks/benefits as well.
Depends. Many will heal on their own. If symptoms are mild or improve without surgery (nonsurgical treatment) it may shrink. Even if it does not go away completely, if symptoms resolve, no "fix" is needed. Surgery is used when symptoms are severe. Injections are sometimes helpful as well.