Do you mean in your miner configuration? Just use 'x' or '123' or similar.
Not the miner configuration. On Kano.is -> Account tab -> Settings -> under BTC Address, there is a required password field. Can't be left blank, can't use some random string like x or 123. BTC Address I'm using my BTC wallet address.
Here's the link to the settings page after you login:
https://kano.is/index.php?k=settingsIf you are changing your BTC address, you need to put in your Kano.is password in that field to change it.