Resin regeneration

In the USA, there are companies that will sell the resin and regenerate it--for a fee. Shipping is a bit of a pain as it must be shipped damp. Still, it is cheaper than resin by a long way.

Resins are regenerated by backwashing them with an appropriate solution. The exact solution depends, among other thing, on the resin.

Once you do this, however, you have to dispose of the solution. This can be ammonia ⇦ on eBay or Amazon [affil link] , hydrochloric acid, sodium hydroxide, etc.

For your application, it's probably just easier and cheaper to get new resin. There are filter companies that will swap out resin tanks for regeneration at their facilities. You basically just pay a fee to have new tanks installed. Try looking for water filter or water treatment companies in your area.