# open/split windows in the same dir
bind '"' split-window -c "#{pane_current_path}"
bind % split-window -h -c "#{pane_current_path}"
bind c new-window -c "#{pane_current_path}"

In your ~/.tmux.conf.

To source it in your open tmux:

:source-file ~/.tmux.conf

Or in any shell:

tmux source-file ~/.tmux.conf