You should use the portal (on the 3rd floor) to go back to the past and meet with the Blond Girl of the past, once you meet them, you’ll know what to do through the dialogue from then on. after the end, if you visit Evergreen again…
Portal Combination Spoiler
A portal back to the past can be opened by aligning the pattern with "N, E, W - Sun, S - Wind". In addition to this, there is one more combination where you can watch additional secret animations. In my case, I figured it out as Brut Force.Personally, I think this quest has a pretty sad story.
If you haven’t seen the Blond Girl event in Evergreen first, there’s nothing you can do in Evergreen in the past. There is a locked warehouse, but LAGS said that the past Evergreen is still incomplete and events in the warehouse are already made, but the next update will help you find the key to unlock the locked door on the map that will be added.