Although in these days we have access to fancy fonts and symbols, in the olden days conventional typewriters had no way of making an umlaut.
A friend of mine solved this problem by taking the "x" key on his typewriter and filing off all but the top bit. This left him with the two sideways dots of an umlaut very satisfactorily. It did, of course, result in his losing his "x" key, but so it goes.
Everyone knows you can't make an umlaut without breaking "x."