He probably bought it online.
Says in the comments "It was from ebay I think,"
The manufacturer is in the US, and only sell a 120V version.
See manual at
https://www.nostalgiaproducts.com/product/tcs2-grilled-cheese-toaster/Any thoughts on how to get this to work on 240V AC ?
I doubt it's wired as two parallel elements, so re-wiring in series isn't an option.
Options I can think of are:
1) add a diode rated for 6A or more, so the elements get half wave voltage.
2) Buy a second toaster and wire them in series, crazy but would work, if done by someone who knows what they are doing.
3) Buy a thick slice toaster that fits the wire baskets
4) Pillage a 240V toaster to suitable replacement elements. (its a lot of work, I'd do it for him if I was in the UK).