The headword is the second person plural, middle/passive imperative (and indicative and imperfect), of the verb presbeu/w (I am the elder, serve as ambassador, pay honor to, but in the middle voice, I go as ambassador); see generally LSJ s.v. It is quoted from Aristophanes, Acharnians 133 (web address 1; see next note), where Dicaeopolis sends Amphitheus away to make a treaty with the Spartans. The scene takes place in the Athenian agora, more specifically the Prytaneum (pi 2999), a public building where ambassadors, both Athenian and foreign, were entertained and honored (Miller, pp. 4-5). The play's hero then tells gawking onlookers -- or, as Henderson (p. 75) suggests, perhaps the very audience itself -- to go away and conduct their embassies.
[1] From the scholia to this Aristophanic passage.
[2] Sophocles, Trachiniae 1064-5 (web address 2): Heracles, accidentally poisoned by his wife Deianeira, implores his son Hyllus to disown her.