You might not have to, actually. He seemed to be aware of his true name, so in his timeline you likely did that already.

[ He gazes out at the sea for a few moments, then back to Marik, but that's enough for Mizuchi to jump out of the water and float over. She curls at Kaiba's feet, wanting to be near her humans. ]

He seemed pleased that we were together, so I think so.