Get Credit memo details by order increment id Magento 2.

You can fetch the Credit memo collection details by Order Increment Id using Magento 2.

When you check the sales_creditmemo table, order_id available in sales_creditmemo table so you first fetch the order entity id from the order increment id.

To get credit memo records, you first fetch the order id by order increment id and pass order id as SearchCriteriaBuilder addFilter() method.