You're holding an event and want the currency that your tickets are shown in at checkout to be something other than the default USD.
- Head to Revenue > Tickets > Settings.
- Click on the dropdown menu under Payment Currency (Beta).
- Scroll to find your currency of choice, or type it in.
- Once you've selected it, press Save.
The currency shown on your event site at registration should update straight away.
Note that you can only show tickets in one currency at a time on your event. So you can't shown one ticket in GBP and another in USD for example.
These setting are event-level, so if you have multiple events and want them all to be in a currency different from USD, you'll have to do this for each event.