–this can be handled in many ways, hope this could help you resolve this
Kindly check you have the below assembly in your xaml, if not add it manually and restart your project and try again.
–For that open the xaml with notepad and we can check whether we have this assembly or not. If not mention the assembly reference, save it and run the process once again
if that doesnt work like you have the reference already available, then in the studio
check whether you have this namespace in the import option. If not import and restart the studio once and try to run the process