How do I display text in an existing label when its ID and text are only retrieved at runtime?

I have many labels on a web page that retrieves label IDs and related text from a database file.  I need to know how to transfer the text to a label on the page with the same matching ID.  For example, let us assume that the label ID of ‘Label5’ is within a string named “mystring1” and the text to be displayed in that label is within string “mystring2”.  What is the C# code that I need to use in order to have Label5 display the text in “mystring2”?
 
Maurice