Does anyone can help me on how to enter the security code for VW RCD300?

I bid for the radio from eBay. I do have the "security code" but I do not have the manual.

So, I do not know which button to press to complete the sequence. I guess I can use the CD 1-4 to enter the four digit code, but which button do I have to press next in order to complete the sequence???

Thank you for any advice on this.