How to modify TTree entry?

ROOT
1

Please, explain the next question.

I’d like to load TTree, modify some entries (with predefined entry index)and save again.
I’s not clear for me how to modify entry.

Thanks!

2

see discussion at:
root.cern.ch/root/htmldoc/TTree.html
look for section
"Adding a Branch to an Existing Tree"

Rene