well first you have to find it, and it can be in diff places for diff installs
mine Was at
C:\Users\EzRyder\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
for the ms store version
then you simply copy the line/entry and move it to the top, then you re number everything to match - personally i might just wait untill wu10 is out, then you will use the method i describe in the post to re order scenery (the content.xml will become obsolete)
note i said ‘Was’ because that file is no longer in use from wu10 on and im in the beta already
[EDIT: its still used but in a different manner, for edited priority only, list is built dynamically now]