You don't need to treat for torn fins- but for fin rot, and if it is, it's easier to move him to a QT tank.
Fin rot the edging will be black and crusty looking, falling off in small chunks.. or white cottony like growth on the edging.
If they are ripped long ways it would most likely be a decoration or the filter is too strong- usually fuses back together after a few days to a week.
If the edges are in a shape of a C or U, sometimes a V, it would most likely be him tail biting.
For torn fins, just keep him in his home, you can up the water change % each week a little to keep the water extra clean to avoid rot. A lot of people use Stress Coat to help promote fin regrowth.
If Ich you will want to do this:
•Symptoms: Betta has white dots (looks like he was sprinkled with salt) all over his body and head, even eyes. Lethargic, No appetite, Clamped Fins, Might dart and scratching against decor
•Treatment: You can treat Ick either conservatively or with medication. Ick is a parasite. Because ick is contagious, it is preferable to treat the whole tank when one fish is found to have it. Ick is temperature sensitive: Leave your betta in the community tank and raise temperature to 85 F. Then you can choose to treat with salt or medication. Conservative: Add 1 tsp/gal Aquarium Salt 3 times, 12 hours apart so that you end up with 3 times the normal concentration. Perform daily 100% water changes to remove fallen parasites before they can reproduce. Replace the water with the right amount of salt. Do not continue this treatment for more than 14 days. If it fails or you do not want to use salt, treat with Jungle’s Parasite Clear, API Super Ick Cure, or Kordon Rid Ich Plus. If your betta lives in a jar/bowl, then it can be difficult to heat the water. There are heaters for smaller containers, but you can also float the quarantine container in a larger heated tank during treatment. Do a full water change every day and add an appropriate amount of medication to the water.
If there is fin rot, then the AQ salt treatment for Ich will also work to rid the rot.
I would just recommend making 100% sure he has ich before going through with the treatment, as excess usage of salt has potential to harm their internal workings, such as kidney failure. It's best to make sure before doing any treatment.
Turning off the filter for the whole period of treatment you risk (well, imo it will happen) killing off all your beneficial bacteria and when you turn it back on, all the dead good bacteria will be flushed into your tank which can be harmful to your little guy..