Chrome release 69 +

To enable flash, click on the padlock icon on the URL:

under site settings, change the Flash from "ask" to allow:

Chrome previous releases

In the address bar, type chrome://settings/content Type chrome://settings/content in the address bar
On the Content settings screen, find the Flash Player listing. Check the status. The Content settings screen
To manage Flash Player settings by site, click Manage exceptions Click Manage exceptions to manage Flash Player settings on a per-site basis
On the Flash exceptions screen, enter the website domain and then choose Allow. When finished adding sites, click Done. The Flash exceptions screen
Close the Content settings screen.

In the address bar, type chrome://settings/content Type chrome://settings/content in the address bar
On the Content settings screen, find the Flash Player listing. Check the status. The Content settings screen
To manage Flash Player settings by site, click Manage exceptions. Click Manage exceptions to manage Flash Player settings on a per-site basis
On the Flash exceptions screen, enter the website domain and then choose Allow. When finished adding sites, click Done The Flash exceptions screen
Close the Content settings screen.