Based on user experience who bought minecraft dungeon through microsoft strore specially the hero edition. You can't install it due to the 2020 10th may upgrade not being released.
its the 15th of July, nearly 70 days past this supposed may 10th upgrade release. Which is not a proper excuse because many people have and still are buying the FLV and are able to play it except for a select few. For whatever reason doesn't have proper evidence that there's been any question put into this other than the "if you didn't like it then you can just refund it" cop out.
https://help.minecraft.net/hc/en-us/articles/360043512292-How-to-Install-DLC-and-Hero-Pass-Content
this link being the explanation on how to install it in the first place, but upon going through the steps there is no ready to install stuff, it is just there in some places and not there in other places.