On Gaussian output graph, do right click on the spectrum and save data in the form of text file. You can plot the graph in Origin software from this data file. You can merge two IR spectra using the same software.

Thank you for your response ma'am. I tried doing the same, but the graph looks distorted.

Good question, I following it.

Hello,

This paper might be helpful:

https://pdfs.semanticscholar.org/2b98/c5fd04ea72487541ce8ae7ca5781087da9c5.pdf