Thank Ivy,
I tried the workflow you suggested, but still getting the missing .xla file error message even after selecting "Yes" to delete from list and reopening excel. It is not permanently deleting and by default when I open a new excel workbook it is searching for the old add-in file which I moved.
I did find a work around. I reinstalled the add-in and made a copy of the .xla file and moved it to the exact location in the error message (original). Then when opening the a new excel workbook I can go under add-ins and uncheck/remove it. Now by default excel is not searching for the .xla file when starting up.