I want to reset my desktop to factory settings but I don't know how. I have tried the general and reset but the reset icon is not there

Assuming you are asking how to reset your Mac to factory settings:

Erase your Mac and reset it to factory settings - Apple Support

And, no...there is no "reset desktop to factory settings" button in System Settings.

Hope this helps.

Why are you wanting to reset your Mac back to factory settings? This Apple document may help if it is why you want to reset: What to do before you sell, give away, or trade in your Mac - Apple Support.

Or, are you having some problems with your Mac? If that's the case maybe we can find out what's causing the problem and fix it. Let us know why and we cn go from there.