How to customize item description summary on mobile devices

[dsm_tech21]

Hello eBay Community.  I have incorporated html descriptions in my listings and they all work without any problems.  But I have not been successful in getting the summary "Item Description from seller" to say what I want on mobile devices. (it seems to be a random pull of copy from throughout my listing, which doesn't make much sense) 

I tried the instructions from eBay posted around 2016 (link below), but all it did was add my description at the top of the html page, but had no affect on item description summary itself .  If a solution has been posted previously, can you please send me the link? I apologize for the duplicate question.  Thanks all, any help would be much appreciated!

https://pages.ebay.com/sell/itemdescription/customizeyoursummary.html