1

I have download the Avast Antitheft On my Samsung Galaxy Grand Quattro …After a few days i have change my sim and now it is showing that the phone is lost or stolen…And it showing that a new pin has send to your first friend phone number…And i have forgett the first friend phone number…Now what Can i Do?

2

Is it not possible to clear the sim card list?
Download the instruction manual - it covers most of the basics like yours

3

You will need to mark the phone as found and add the new sim to the trusted list.
http://files.avast.com/files/documentation/mobile-security-user-guide-en-v2-4-updated.pdf