To start you need to have the filter cleaned out by what it called a manual regeneration. It’s not a warranty issue. Take it to a Subaru dealer and get a quote from them. The reason the light has come on is that the car hasn’t been driven in a way that ensures the regeneration takes place automatically. It could be because of the way you drive it, or the way previous owners have driven it. When you talk to the Subaru dealer about regenerating the filter also ask about the way to drive it so the regeneration happens automatically.