how to completely factory reset my phone without messing it up?

So basically me, the stupid idiot, rooted my phone using Kingroot. Bad choice. Now I want to completely factory reset my phone. My friend suggested flashing it twice and then resetting it. How do I do it? Phone: Samsung Galaxy S3 mini Model: GT-I8190 Version: 4.1.2 Baseband version: I8190XXAMG4 Kernel Version;: 3. 0. 31 - 1332988 se.infra@SEP-110 #2 SMP PREEMPT Sun Jul 28 14:54:47 KST 2013 Build number: JZO54K.I8190XXAMG4