In MyArena, under Stream Configurations, if you scroll down you will see the Scorebar and the Production overlay options.
Once you have created your overlay and upload it to the Cloud, you can select it from the - select - menu and click on Import.
If you have created several overlay, after you have imported them all, they will all be in the list under None - Do not use any overlay for you to choose.
Note that one overlay is per league. So if you want the same overlay in several leagues, you will need to do this in all the leagues' stream configurations.