Hi, I need a master unblock code for my Samsung galaxy S6. Where can I get it?

Jul 7, 2018
2
0
10
I accidentally put in wrong network code. I have the correct one. But now it says it needs a master unblock code. I read a thread here that described how to input 8 instead of 7 digits but didn't understand it. Can someone please explain step wise How and where to get master unblock code? Will be much appreciated. Thank you so much.