If all FRFs have the same frequency base then you can open 1st one with Excel and simply add the Data (Gain and Phase separately in Bode case) as next columns.

Dear Niladri Sekhar Barma ,

What is the purpose of combining the different frequency responses.

Are all the frequency spectrums cover the same frequency range?

Do you want that they appear distinguishable from each other then you can overlap function in Excel graphs. To implement overlap please follow the u-tube:https://www.youtube.com/watch?v=AjCDYXk6NkE&ab_channel=MyExcelOnline.com

Best wishes

Dear Abdelhalim abdelnaby Zekry , My sole objective here is to get the generalized FRF from the set of different FRF data files which corresponds to different transfer function. After getting the generalized FRF, I also have to curve-fitting it to get a smooth curve of FRF.

Thanks