So, MS have removed Automator functions for Excel 2016. Thanks.
Note, my output filename is hardcoded because I use this file for printing labels with a Dymo Labelwriter that needs to know the filename before hand.
Here’s my workaround:
on run {input, parameters}
set docFolder to path to documents folder as text
set old_file_name to input as text
set new_file_name to docFolder & "new-file.xls" as text
tell application "Microsoft Excel"
activate
set theWorkbook to open workbook workbook file name old_file_name
set theWorksheet to worksheet 1 of theWorkbook
save as theWorksheet filename new_file_name file format Excel98to2004 file format with overwrite
close active workbook
end tell
return docFolder
end run