Where is the iphone 7 ring switch?

The Ring/Silent switch is on the left side of the iPhone 7. See the following illustration from Use the side button, Home button, and other controls on your iPhone - Apple Support

It is item 3 in the illustration. The rest of that support article may also help.

This is primarily a user-to-user support forum; other Apple users like you.

Up is toward the front of the phone (the glass screen); down is toward the back of the phone. If I remember the iPhone 7 correctly you may need to use your fingernail to do that.

Regarding your quotes:

I was forced to buy one and the "Apple-store" didn't bother to provide me with the mos basic information.

and

You expect me to spend hours looking up the simplest operation?

The arrogance!

You bought a used iPhone 7 from someone. Apple hasn't sold them for at least 5 years. No one here sold it to you and no one here forced you to buy one. This is primarily a user-to-user support forum; other Apple users like you.