Hi Lizzy,
a 500a and 503a are 2 classic US machines from during the space race so they have very iconic styling and get called the 'Rocketeers'
Something like this:https://www.ebay.co.uk/itm/VOLTAGE-CONVERTER-TRANSFORMER-STEP-UP-DOWN-200W-240-230V-TO-100-110V-VICEVERSA/250725568129?hash=item3a60688e81:g:gsAAAOSwrjhavC6u&frcectupt=true
Should do the current changing and I have a 2 pin vintage style US plug - admittedly in retro brown to suit the 503...
Definitely dont write off your machine with a little time and love it'll be a beautiful little stitcher that you got at a bargain price
R.