Find the area in the contested Covenant District where the actuation scroll "should reside" ( -166, -1, -171 ) /waypoint -166, -1.22, -171, meaning, you get an overhead message. There is a mob there, you can ignore the fight and use the periapt to zone the group away.
Use Jorlak's Chrono Periapt. This will teleport your group back in time to the city of Skyshrine before it was destroyed/ravaged.
Cick on the jar at ( -187, 0, -166 ) /waypoint -187.27, 0.00, -165.76 inside an alcove.
There must be some way to open the Gate Caller scroll jar. Travel to ( -33, -0, 9 ) /waypoint -33, -0.41, 8.60 and kill a Draconic Gate Caller. (It has a 15 minute respawn timer.) Careful of AoE, avoid pulling epic guards.
Go back and click on the jar again at ( -187, 0, -166 ) /waypoint -187.27, 0.00, -165.76.
While you're there, there are two statue quests you can get by clicking fountains to recieve heirloom petamorph wands. Look for glowing statues when you mouse over them.
While you are time-traveling to the ancient version of Skyshrine, you can save time by picking up the six quests in the districts. These are obtained by clicking statues or fountains (see the Skyshrine Timeline for details).