$-link globalin the channel you want to link. The only requirement is that the server has at least 20 members (bots don't count). This requirement exists to prevent people from linking channels that will rarely or never get used, because it sucks up the bot's resources and makes it slower for everyone else.
$-unlinkin the linked channel.
$-link private namein every channel you want to connect. For example, if you're linking the general chat of 2 or more servers, use
$-link private general. If its the staff chat, you can do
$-link private staff.