Want to unlock network on old galaxy s6

Okay. Have you inserted your SIM card to the phone, *****?

Okay. Just to double-check, is the phone turned on now?

Alright, good job!
I'd really appreciate it if you will follow my instructions

1. Open the Settings app
2. Tap Biometrics and security. Or it should be called just
   Security
3. Tap Other security settings
4. Tap Set up SIM card lock
   There should be a button to remove a block from a SIM Card
   Should look like that.
5. Enter your SIM card PIN, then tap OK. The default PIN number will depend on your network provider. You can also find your SIM card’s PIN number on the original packaging it came in.

Is that brand new? Do you still have a box?
What is the carrier? What is the name of the phone service provider, *****?

The default pin is either 0000 or 1234.
Try both, please

Yes, change it and remember the PIN you are going to set up, *****

Alright. Is the network service is now visible?

Got it, please reboot your phone now

Let me know when it is done, and it is back on track