Surp Astvazazin Armenian Church is at  Dadyan street in Bakırköy district. Next to Dadyan Armenian Elemetary school..
Bakırköy Surp Astvazazin Armenian Church- Google Maps

First of all you should reach Bakırköy center.
How to go distinct of Bakırköy?
You can come by IDO Fast Ferry from Bostancı, Kadıköy, Yenikapı, Avcılar district to coast of Bakırköy district.
You can come by Metrobus, you should get off Ömür station then you can go by foot or by minibus to Bakırköy centre.
You can come by yellow minibus from Taksim.
You can come IETT bus to Bakırköy center.

After you reach to Bakırköy center,
If you are coast of Bakırköy, you can walk from next to Mado patisserie road up to Bakırköy center 5 minute, you can see left part of road.
If you are center of Bakırköy, you can walk to road of coast after 10 minute you can see right part of road.