The Costumes/Guardian stones of acquired Epic/Legendary Grade are obtained in a pending confirmation status.

During the pending confirmation status for Costumes/Guardians, they cannot be confirmed through the card list. When accessing Costumes/Guardians, you have to decide whether you want to replace the stones on the pending confirmation page to finally obtain them.
(1) Go to Costumes/Guardians > Pending Confirmation Items
(2) Click on the acquired hero-grade or higher costume/guardian > (Proceed with resummon) > Final Confirmation

You can select and confirm one desired card among the results of multiple resummons. Depending on the card grade and number of attempts, Dias are consumed.  During the pending confirmation status, you are given 3 chances to change to a different costume of the same grade.

If the confirmation time expires, the most recently drawn stone will be confirmed. Adventurers can decide if they want to resummon.