There is no any tool available for direct conversion Excel file to .arff file. You should follow some steps to convert Excel file to .arff file.

The following steps can solve your problem

Save your .xls file in .csv format.

Open the Weka GUI Chooser and then click on the tools button in the top menu bar.

Click on the Arffviwer

Choose file types to be loaded like, *.csv, *.data

Open *.csv file to view the data and values

Name the file with the .arff extension

Save the file

Thank you İbrahim Emre Tastan your solution (answer) has indeed solve my problem.

Thanks indeed