I have forgotten my iPhone 7 passcode, and I can't go into recovery mode.

I have forgotten my iPhone 7 passcode and been watching youtube videos about how to reset to factory settings. All suggestions begin with connecting phone to I tunes on a computer. I plug my phone in and it says unlock phone to use accessories and is not picked up by the computer. I can't unlock it because I don't know the passcode! I've also been trying to put in recovery mode but I do that and all it does is turn back on saying iPhone disabled try again in 15 minutes. So any advice on how to get round these difficulties? I would greatly appreciate if you could help me out!