Organic traffic dropped off after migrating to WordPress from Shopify

My boss recently migrated to woocomm from shopify for more control of the site and user experience.

However according to ahrefs it looks like alot of her organic traffic has fell off since.

The domain was transferred over but the shopify site is still live with its myshopify domain

We contacted a few seo agencies but they want to charge thousands for the "seo migration", we're wanting to save costs and would greatly appreciate any advice you may have for doing the migration.

Is it as simple as redirecting the myshopify URL to the new WordPress site? If there's any other best practices we would gladly appreciate the help and I can paypal you some $$ for your time also!