Hi I am trying to connect my Blink camera to my Alexa app and it tells me I have to put a pin number
That’s correct, it wants you to create a PIN, there and then. You will need it later, for Alexa commands. It is not asking you what the PIN is. If I recall, it is very badly worded/presented, leading someone to believe it is asking for the current PIN, of which there is none, because you haven’t set it yet. This is the PIN setting step.