On a Mac, you do not need to switch to a German keyboard to type an umlaut. Hold Option + U, release it, then press the vowel: Option + U followed by a gives ä, by o gives ö, and by u gives ü. For capitals, add Shift after the dead key: Option + U, then Shift + A for Ä, and so on. For ß, press Option + S.

If you are on a shared machine or a keyboard without those shortcuts, copy the letters instead. Umlaut Letters is a free copy-and-paste page for German learners, writers and designers, with keyboard shortcuts and Unicode, Alt and HTML codes in one place, so a name like Müller or a word like grüß keeps its exact spelling.