Add into ~/.tmux.conf
set-window-option -g mode-keys vi
bind-key -T copy-mode-vi v send-keys -X begin-selection
bind-key -T copy-mode-vi y send-keys -X copy-selection
bind P paste-buffer
copy to clipboard
CTRL+B [
and then move cursor to start of area which you want to copy.
pres key v
to make selection
when you select wanted text press key y
done: text is in clipboard
pres ESC
and Enter
to return back to promp
paste from clipboard
pres CTRL+B P
done