Thank you very much for your reply!
I followed the steps mentioned using ENVI Classic and am sharing some of the results with you.
First, I chose the 62231 ASCII file and converted it to a spectral library using the RELAB ENVI header file information, which I found here (https://lost-contact.mit.edu/afs/enea.it/software/rsi/envi_3.5/spec_lib/igcp264/igcp_2.hdr).
Once that was done, I tried to match the same with a small region that I was able to subset from one of the M3 (Level 2) images. Unfortunately, I am still unable to match the two spectra.
Please let me know where I am going wrong.
For your convenience, I am attaching some screenshots.