Unable to Activate after replacing battery

Background:

She dropped it into water last April, and it stopped working normally. She said that the battery was not charging at all. She had it “inspected” by a non-accredited service shop and she told me that she didn’t ask to replace any of the components.

However, prior to replacing the battery I noticed that the battery connector bracket and front panel assembly bracket was missing. So I’m not 100% sure if this could mean parts were exchanged during the “inspection”

Battery Replacement

Before I replaced the battery, I tried turning the iPhone again. When that didn’t work, I plugged it in and turned it on. This time it showed the Apple Logo, then the red low battery charge icon. I left it for 15-20 minutes but the charge didn’t increase and then I decided to change the battery.

After the replacement, I turned on the iPhone and got an Apple Logo, then a blank screen, I knew the LED screen was on because of the soft light around the edges of the screen. I then connected it to my Mac and iTunes, which prompted me to do a Restore or an Update. This was the message that iTunes was showing me:

So I went through with the update but it still gave me the same message. I tried a restore as well, no luck. I figured there was some kind of activation lock going on or something.

What is puzzling to me is my sister said she didn’t erase the phone, so I was expecting the phone to go into the lock screen asking for a passcode. I was wondering why it suddenly wanted me to do a restore/update? Could I have broken something inside while replacing the battery?

Steps I already tried:

1. Restarting/Shutting down the iPhone before re-trying the activation
2. Did a restore & update in iTunes while in recovery mode
3. Inserted my own SIM from my iPhone X into the iPhone 6

At the moment, our remaining option is to get my sister’s SIM card into this phone hoping that would activate it.

In case that still fails, is there a way to activate this iPhone without paying for service at an authorized service center?

Thank you!