What is the issue?
Flash is an unsecure technology. Users are encouraged to block sites that use Flash because of security issues. Also, search engine crawlers are not able to crawl Flash. Any text on a web page configurated by Flash will be invisible to search engine crawlers, meaning the page will not rank on Google.
How to fix
Use HTML5 instead of Flash.
Content delivered by Flash plug-ins can be insecure and unsupported by browsers so it's unlikely your page visitor will be able to view it. This can cause high bounce rates for your page. Use Google Analytics data to find pages with high bounce rates so you can prioritize which pages to fix first. Learn more this article.