TRUNCATE TABLE `prefix_sales_flat_order`; TRUNCATE TABLE `prefix_sales_order_tax`; TRUNCATE TABLE `prefix_downloadable_link_purchased`;There is no need to manually ALTER TABLE 'xyz' AUTO_INCREMENT=1; since TRUNCATE rebuilds the structure of the table and sets AUTO_INCREMENT=1 automatically.
Please note do perform such actions on test deployment and have backups prior of doing such actions!
Delete Magento test orders
Delete specific Magento RMA
Delete all Magento RMA