Hi, Raghava@rock!
Hopefully it does if from the left instead of from the right, otherwise it wouldn't be working as the manuals, the documentation and the help both built-in and online say.
If that text is in A1, try this:
=SUSTITUIR(A1;",";".";LARGO(A1)-LARGO(SUSTITUIR(A1;",";""))) -----> in english: =SUBSTITUTE(A1,",",".",LEN(A1)-LEN(SUBSTITUTE(A1,",","")))
Just as a tip, remember that if you enter in an empty cell "=XXX(" (unquoted) and press the "fx" button at the left of the edition bar text box, you'll be prompted with the function wizard which shows every argument, gives a brief description of the function and by the bottom left link lets you access the built-in or online help. It works for any function.
The same from the VBA editor, you can place the cursor (keyboard, so click, don't hover with mouse) on any VBA reserved word and press F1 to access the same type of help.
Regards!