On iPhone 7 where is security

No, if you are doing automatic iCloud backups it won’t do so until in the Lock Screen (this is when you iPhone goes to sleep and has a dark screen), is connected to power and has a WiFi connection. Unless you have changed your settings to never lock your screen you don’t need to do anything.

Could you help us with some details of what you are looking for or trying to do?

I'm not sure why you need to do this but just click the power button.