From Longman Dictionary of Contemporary Englishfreshen up phrasal verbWASHto wash your hands and face in order to feel clean and comfortablefreshen yourself up Fiona’s gone to freshen herself up. → freshen→ See Verb table
Examples from the Corpus
freshen up• The bathroom's on the right if you'd like to freshen up.• She hoped there would be time to freshen up before the interview.freshen yourself up• It wasn't vanity that had prompted her to freshen herself up. 