SEO optimizer/editor I would sugeest to do this manally and not have a app do all the work
Why if the page has the incorrect info this could throw off the optimization.
Ive been using ReloadSEO recently and quite like it.. it's expensive for what it is IMO, but I feel it's been a good way to get a feel for what I need to work on.
Actually, there is an app that does exactly this. Experimizer (https://apps.shopify.com/experimizer) is a free tool in the Shopify app store that will automate the SEO and Social Sharing for you. We basically figure out what combination of information from your site will help you become more discoverable on sites like Google, Facebook, Pinterest, etc. as well as what customers respond to the best so that you can drive more traffic to your site. Experimizer learns by itself what the best optmization is and continously runs in the background to make sure that the optimization stays up to date.
It's an easy to install and free app that sounds like it does exactly what you're looking for. If you have any questions let me know!