On his Google+ page, Google’s John Mueller made clear that HTTP/2 has no impact on SEO:
“HTTP/2 has no impact on SEO. Search engine crawlers (even if they don’t support HTTP/2 yet, like Googlebot) will continue to work normally, you don’t have to set up redirects, change links, add markup, or make any changes in Search Console.
Most browsers only support HTTP/2 together with HTTPS. That’s when users will usually see improvements. Already on HTTPS? Awesome, you’re all set.”
There are other things that have a much bigger influence on the positions of your web pages in Google’s search results.