Device for repair not showing in MS account?

These are devices tied to your MS account. Go to https://account.microsoft.com and log into your MS account. Then you should be able to navigate to "Devices." You can remove old devices from there by clicking "Show Details" under the item you want to remove.
Then under the picture of the item at the top is "Manage" and it will be a drop down menu with the option to remove.

I am logged into the Microsoft store and it shows that Minecraft is owned. However, I cannot download it because the device (repaired computer) is not linked to the account.

Register the serial number of your Xbox and/or Kinect Sensor on your Microsoft Account "Devices" webpage, and go to "More Actions" > "Schedule a repair".

Follow through the process as though you were actually setting up a repair, and it should eventually show you a repair price.

Do it all here: https://account.microsoft.com/devices

Hi, if you need to get your Xbox repaired, MS can do it. Please go to https://account.microsoft.com/devices/ and check whether your device is under warranty. You can also get it booked in for a repair there.

Hi there,

usually you will be able to check the warranty when you add a device to the devices list and it will show the warranty for that device, this is the link:

https://account.microsoft.com/devices/

When setting up a repair request it usually will also show the warranty, this can be done via the same link, but it's advised to only do that when you actually need a repair request for a device