Unable to access Time Capsule with forgotten password to erase all the data

I replaced a MacBook Air with a newer version and at the same time I stopped using my Time Capsule and started using iCloud for storage. I now want to erase all the data from my Time Capsule in order to recycle it.

I have connected the above Time capsule, to what is effectively a new MacBook air, one that has not been connected to before. It is asking for a Passcode - I was unaware that I has set up a passcode for it and if I did don't remember what it was.

I have checked my key chain and there is nothing in that and I have also tried 'tmachine' as suggested by a google search. Please can someone advise me, a non technical user how to proceed. Thanks!

[Re-Titled by Moderator]