The headword is the aorist imperative active, second person singular (and aorist indicative active, third person singular), from the verb problw/skw, I go, come forth, come out of the house; see generally LSJ s.v., and (for the simple verb) mu 1192. The entry comes from a scholion -- see next note -- on Homer, Iliad 18.392 (web address 1), where the elided headword appears: pro/mol' w(=de, come this way, come thus, come as you are. In the Homeric passage, more fully at eta 656, Charis requests of Hephaestus that he come forth from his workshop to greet their unexpected guest, Thetis; see Edwards, p. 192 and the note to eta 656.
[1] The gloss, which follows a scholion (= D scholia) on Homer, Iliad 18.392 (web address 1), is the same form as the headword, but from the deponent verb proe/rxomai, I go, come forward; see generally LSJ s.v. The headword is identically glossed in Apollonius' Homeric Lexicon (136.23), Hesychius pi3586, and ps.-Zonaras 1588.4.