The explained steps in this Guide will help you to Factory Reset Samsung Galaxy S2 with model numbers:

Samsung GT-I9100. Samsung GT-I9100G. Samsung GT-I9100L. Samsung GT-I9100M. Samsung GT-I9100P. Samsung GT-I9100T. Samsung Galaxy S2 GT-I9100 Factory Reset Checklist:

1- This process restores the Android platform to its original state and wipe all your data, So backup all the wanted data (Contacts, SMS, Photos, Videos,… Etc).