unable to do it
I think you meant the Excel Splitter featured app or Excel Merger app, right? I tested using the Excel splitter app with some files and it works fine. I uploaded the file to the app and clicked Split after selecting XLSX in the Save As combo box. It does split the Excel file by worksheet. I downloaded the zip file containing the Excel file and it works fine.
Is the sample file you uploaded only have one worksheet? Please note, the splitting app is to split a large file containing multiple worksheets to save multiple Excel files (each file is based on single/separate worksheet). Do you think of Excel splitter something different? Did you get any errors occurred during your operation, please specify? Also, if you can provide sample files, splitting resultant files, and merged resultant files. This will be very helpful for us to locate the issue. We will check it soon.