We found a solution it's not that easy and you need a certification previously created at your PC
- open your partner center select your target app/game and click 'Package Identity'
- open your VS solution double click 'Package.appxmanifest'
- At packaging tab fill 'Package name' same as Partner Center also fill 'Publisher display name' must same as Partner Center.
- Click 'Choose Certificate' button if your device has certification installed previously select the certification file. (I don't know if you don't have a matching certification file I assume it won't work)
- And finally, select 'publish' and 'create app packages' and select 'sideloading' click next.. follow menu and create package.(don't forget to set 'Generate app bundle to 'always')
- When finished you will have a 'appxbundle' file at your outputlocation upload that file to Partner Center. it should work.