Looking for an SEO Expert to help me restore my website

I have a ~17 year old site that did really well for most part of its existence. However, I migrated the site to a custom built platform and the site slowly lost the traffic. There is no manual penalty (never had any) on the site and has tens of thousands of backlinks.

I have over 10 years of SEO experience and I think I know what's wrong with the site. I however am hard pressed for time and want to work with someone who's a proven record of restoring website traffic.

Instead of doing it all by myself, I want to partner with someone to fix (the shit I created) and restore my site's traffic.

If you know someone who can help, let me know in comments.