Harry realize that Scorpius an Elvis were traveling in time after what

Albus Potter and Scorpius Malfoy were two young wizards who travelled from 2020 to 1994, to try and stop Cedric Diggory from being killed by Lord Voldemort.

ok correction its not Elvis, its Albus.

Harry realize that scorpius and albus were travelling in time after what ?

when albus and scorpius travel back to the triwizard competition second task, moaning myrtle tells harry that the boys were asking for a way to the lake and they had a thingy which she describes to be the Time Turner. There Harry realizes that albus was eavesdropping to his and amos diggory's conversation hence they are currently time traveling to save cedric