I want go back, how to change ctrl-t to ctrl-o ?

[gaoyuqiang]

Go back's shortcut ctrl-t works. How to change to ctrl-o?
I try to write it to .vimrc, but it can't work.
map <C-o> <C-t>$
What is the right way?

[gaoyuqiang]

It can work. Because I put .xvimrc to a wrong place.