Deleting and renaming a single column until a certain row in emacs -

Deleting and renaming a single column until a certain row in emacs -

i have big emacs file. in file there column lists "b". want alter column list "a". possible in emacs without manually clicking , renaming? don't know how write script i'm not sure. i'm not best programmer.

the rectangle commands might work here. set mark on first line, in column change. navigate lastly line, 1 column over. type c-x r t (string-rectangle) , come in "a" @ prompt in minibuffer. replace text in rectangle corners defined point , mark text you've typed in minibuffer.

emacs