The current Version of DeviceCommander is using .NETCore3.1. The "older" Branch, based on .NETCore2.1 will no longer get any feature updates.
If you want to update your existing installation, just follow this guide:

Disconnect

If you have deployed your DevCDR Instance using the "Deploy to Azure" button, your Instance is linked with the GitHub repository.
If you open the WebApp in the Azure Portal and switch to "Deployment Center", you will see the Repository and the Branch:

As there is no option to just change the branch, you have to click on "Disconnect" to remove the SourceControl binding...

Note: Your instance will not update automatically if it has a Source-Control binding, you have to click on "Sync" to get the latest version!

Deploy

Once the Source-Control binding is disconnected, you can create a new connection:

Select "External" in the "Manual Deployment (push/sync)" options.

On the next Screen, select App Service build service:

On the 3rd Screen, you have to enter the Repository URL: https://github.com/rzander/DevCDR and the Branch ServerCore31. As DevCDR is a public Repository, select Private Repository = No:

Sync

The WebApp will get the Source-Code from GitHub to compile and deploy the latest version... This may take a "moment"...

Once it's finished, you should see the Status as Success (Active):

Note: Don't forget to Sync from time to time to get the latest updates and fixes!