SEO Strategy for Established Authority Site

Hey all,
Looking for a bit of advice from the BHW community. Currently running an established (old) authority site, which has a huge level of branded/keyword organic traffic landing on the main site index. We've never built out SEO for the site in the past, but have got thousands of legitimate backlinks, social shares, etc.

We've now launched some new functionality on the site (basically new pages) which we would like to try to rank for specific keywords unrelated to the main keyword…

SEO Strategy for Established Authority Site