Alex was only aware that he had woken up here, confused, as the memories of things to pass flooded his mind. They never talked about the how.
Even David was unsure at first. After the memories had been fully integrated, it took him a while to understand why he had found a chain on himself that he had never bought.
It had taken even longer for him to understand how this was even possible. In his memories, he died too early in the apocalypse for anyone to be strong enough to pull whatever they had to send him back.
Especially since he was dead.
It made no sense to him for a long time.
That was, until he saw Chronos again, and saw what he was able to do now.
Xavier was using time magic on such an advanced level already, something he had barely started to master in his old timeline. But it had made him realize something.