:s/a/b/
Swaps the first occurrence of a for b before running.
The long form of the caret line: it substitutes the first occurrence of one piece for another inside whatever the designator brought.
Its advantage over ^a^b^ is aim: it hangs on any event — !ssh:s/estufa/campo/ fixes a command that isn't even the last one.
$ systemctl status estufa.service
● estufa.service - inactive (dead)
$ !!:s/status/restart/
systemctl restart estufa.service