@SLIN Welcome to Q&A forum. I understand that you are looking for a sample code mentioned in the video which you have shared.
If you have uploaded the app mentioned in the video in your workbench, you should be able to see it in the Xamarin app as well as shown in the video.
All the samples related to Azure Blockchain are available here: Microsoft Azure Blockchain Workbench samples
Also, please check this sample project contains a native iOS and Android application built with Xamarin.Forms for Azure Blockchain Workbench.
Hope that helps. Do let us know if you have any further queries.
Please accept helpful responses as 'Answer', which will be helpful to others as well.