To change the store currency of your Etsy store, go to Shop Manager > Finances > Payment Settings > Currency.
You can read more on how to do this and how this affects you in Etsy's Help Center here.
After changing your Etsy store currency, remember to click "Sync products" on the page with your store products in Gelato. Without this step, Gelato will be creating new products using the wrong currency.
You can change the billing currency of your Gelato account as well. Read more on how to do so in our article How can I change the currency in my Gelato account?.