Hello Xbox fans!
When word got out that Beam was going to be on Xbox I found it to be pretty cool. However, upon loading the app for the first time, it created a Beam account automatically using my Xbox Live account. Problem is I already have a Beam account and thus I was (for a while) using two Beam account.
I finally saw in the Xbox Beam app that you CAN use your current Beam account on Xbox. Here is how:
- Load the Beam app on your Xbox.
The first time I loaded the app, it created a new Beam account using my Xbox Live credentials.
- Select your Beam profile. (top right - purple/blue circle)
- Select "Link to a different Beam account."
- Go to the link as shown and log in your Beam account (Your main one that you used before Beam was available on Xbox.)
- Then enter the code that you see generated by the Beam Xbox app.
- You will be prompted to select witch account you want to link your Xbox Live account to.
Important: Make sure you select the correct one. 
- It will ask you what you want to do with the old one "aka the one that Xbox created for your the first time you opened the app". I decided to delete the one created by Xbox the first time I opened the app. But you can keep it if you want.
- Once your account is linked, return to your Xbox, hit the B button then you should now see your actual Beam account.
Hope this helps!
Happy steaming!