Hi Calvin and welcome to CA!

You have two options.

1, Use a US 110V to UK 240V converter. These plug into the mains power outlet at the wall and you then plug the Amiga's power cable into it. It will convert our 240V power supply into a 110V one your Amiga's US PSU can handle.

2, Replace the Amiga's PSU. This is the option I would go for. Replace the original US Power supply Unit (PSU) which is inside the A2000. You can get adapters to connect newer PC PSUs to an Amiga and this will then allow your Amiga to work with UK 240V power. It also has the advantage of completely replacing the Amiga's old PSU which will now be very old and wearing out. A new PSU will help preserve the Amiga for longer.