I have 4 lines incoming on my phone line 4 used to have a different ring than the other 3 this week line 4 started ringing with the same ring as the other 3 in the manual under ring type, it says to select distinctive type ring to choose feature*6, press next to select ring type, and OK to store. But this changes all the lines not just line 4, How do I change only the 4th line.