In 1969 the growing Indian Navy couldn't achieve enough officers through education at the Royal Navy in Darthmouth and made their own Naval Academy in Cochin (now Kochi). Their need for training ships caused rebuild for the three Leopard Class vessels where the aft canon was removed and the superstructure was lengthened with a classroom with a helipad on top. It hasn't been able for me to get the exact date when the rebuild was finished, but in 1975 all three had their final look. I haven't get information either if it was at that time Beas and Betwa changed their pennant numbers (from F137 & F139 to F37 & F39), but I will call it a qualified guess
They served as operative frigates as well as training ships untill decommision except for INS Beas which was pure training ship her last two year.
Here they are: