Acho que você está procurando join-pane
:
join-pane [-bdhv] [-l size | -p percentage] [-s src-pane] [-t dst-pane]
(alias: joinp)
Like split-window, but instead of splitting dst-pane and creating a new pane,
split it and move src-pane into the space. This can be used to reverse
break-pane. The -b option causes src-pane to be joined to left of or above
dst-pane.
Você pode usar isso com a linha de comando ( C-b :
).