I suppose that the numbers were added with the plug-in Number Repeated Measures - right?

(Plug-ins menu > Measures > Number Repeated Measures)

The plug-in creates the numbers as expressions.

Switch to the Expression Tool, and handles will appear on the numbers.

You can remove an expression via its handle.

Another - more general - way (which also works for many other items):

Selection Tool.

Double-click on the number.

Finale will switch to the tool that created the number (= in this case the Expression Tool), with the number handle selected.