The place to start would be letting the board know what code(s) have been associated with the check engine light. They are in the format P0123. Check you invoices as they may have been recorded. If not many auto parts chain stores will read them for free. If you do have the invoices handy also try to be more specific about what has been repaired/replaced.
You also don’t need a dealer. Most any reputable local mechanic can do the work and normally for a lot less.