Join two tabs (also called panes) in Byobu by calling running a tmux command.
Call the Byobu tmux prefix (Ctrl + a) followed by a colon.
Ctrl + a + :
At the prompt, run the join-pane command with the source panel using the -s flag.
:join-pane -s 2
This will split the current window horizontally with the current window in the top and the window in position 2 in the bottom.
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.