How to export a package for Xbox?

Hello all,

SUMMARY: How to you export a package from Unity to Xbox?

DETAILS: I have been working on an indie game for several years now, and I released it to Steam earlier this year. I have been working hard on porting it to Xbox using the Microsoft Partner Center. It is asking for a package; this is the text of the prompt:

"Drag your packages here (.msix, .msixbundle, .msixupload, .appx, .appxbundle, .appxupload, .xap)..."

However, the only way I have been able to create a package is on the Asset menu -> Export Package, which always creates a file of type (.unitypackage). I have no idea how to convert this to one of the above formats, or if there is another way to export a project. I also am unaware of any alternatives to providing a package. This is the error message I get: Does anyone have a solution? I would really appreciate it.