s6-instance-control sends commands to a running instance of an instanced service.
s6-instance-control [ -wu | -wU | -wd | -wD | -wr | -wR ] [ -T timeout ] [ -abqhkti12pcyroduDUxO ] servicedir name
The options, and the commands they represent, are exactly the same as the ones understood by s6-svc.
In fact, s6-instance-control is nothing more than a call to s6-svc on the service directory representing the name instance. It is syntactic sugar so the user does not have to depend on the internal representation of instances and the location of instances' service directories.