You can buy the umlaut for a quid (plus delivery).
Get a baking sheet and iron it on for 30 seconds.
https://www.ebay.co.uk/itm/146281859313?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=piFRazZRRuK&sssrc=4429486&ssuid=oXOPAbMMRM-&var=&widget_ver=artemis&media=COPY