You can easily change the store currency in Wix from your Wix dashboard by going to Settings > Language & Region in the Site currency section.
After changing your Wix store currency, the change will not be reflected in Gelato. Any new products will still be created in the original store 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?.