The system automatically generates their username and password which are a random sequence of letters and numbers. You can edit these details for them via the following steps:
Find out the club auction site they are wanting to bid on and log into the club console:
Auction > Members > Search for the member based on their first or surname > Edit > Username/Password:
I recommend to change their details as well
Username: The customer username as one word, example: AnitaMarchionna
And advise them that once they are logged into their account, they can edit these details to something more memorable via Edit Account and scrolling down to the bottom.