Simply saying, you can't. Only through more sentences and context can you distinguish whether the umbrella's owner is a male or female. Think of it as the usage of a genderless possessive pronoun. Spanish has it, as in "su paraguas" ("his/her umbrella). Chinese has it, as in there is no Chinese character representing a possessive pronoun to differentiate between genders. In English, however, we have gendered possessive pronouns, as in "his" and "her".