The Bolt Merchant Dashboard allows you to issue full and partial refunds. However refunds processed through the Bolt Merchant Dashboard will not sync with your Shopify order management system. Given that numerous contents of your Shopify store are linked to a specific order, such as inventory management, it's best practice to issue a refund from Shopify itself. Simply select the transaction from your orders and click refund. Below is an image of how to do so. This will update the transaction in Bolt as well to keep the order in sync.
You can use the Bolt Merchant Dashboard to issue a refund if necessary. Simply, select the transaction that's affiliated with the given customer and select issue refund to do a partial or full refund.