Hi @jais1609,
Firstly save and close xaml file by leaving error message as it is. Now you’ve to open the xaml file in Notepad and add below assembly reference manually (Copy-paste in that notepad) save that notepad, and double click on xaml file to open it.
<AssemblyReference>System.Data.DataSetExtensions</AssemblyReference>
Follow this thread, it’ll help you.