Head to the marked location and examine the scope to get the mission started. After the cutscene, drive to the New Dawn temple and sneak inside. You have to hack one of the two access key sources to be able to be able to open the doors of the temple building. One of them is from a laptop inside the security office. The temple yard has several guards but most of them are far in between and can be isolated away from each other. If you want to preserve your stealth approach, make sure to employ stealth melee combat or silenced weapons. Like before, you can also use your quadcopter to scout and tag the guards around the temple or use it to disable/kill the guards by dropping ESDs and IEDs as well as remotely luring and setting off proximity traps.
Once inside, go to the second floor office and access the security router. Route the data flow properly so you can access the secret lift leading to the Sumerian tablets underground. This puzzle should be fairly easy but if you need help, refer to the video below. Approach them to trigger a cutscene. Leave the mission to complete the objective.