Speed improvements on mobile webpage.

Got a client ive worked with for over a year who wants his mobile SEO rating to improve. Fully willing to pay but wants actual results. Anyone replying here ill happily send forward.

His request:

Our Wix site www.betterspeech.com ,
gets 22 on mobile on Google’s PageSpeech Insight https://pagespeed.web.dev/

We are looking for an expert SEO/JavaScript or Wix Velo developer that can optimize whatever can be possibly optimized on the site and its code to reduce the First Contentful Paint (FCP) from 3.6 seconds to under 2.2 seconds to help improve conversion and our SEO rankings.
If you are 100% sure you can achieve this task please reply.
Tx, Ranan