This use to be a simple matter of writing out a cheque but no on has cheque books anymore. If you do still have a cheque book it is a simple option. Otherwise, we need to do it some other way.
You are unlikely to be able to transfer the money from your phone banking app as the deposit is likely to exceed your daily limit.
Some agents have an arrangement with their bank where they have an app which allows you to enter your account details and approve it to draw the money out of your account.
Another option is you can get a blank bank check form from your bank that you fill out after the auction if you are the winner.
Cash might work but it is not a great idea…
The only other option is agree with the agent that you can pay a small holding deposit of say $5,000 on the day of auction that you can transfer from your phone and then you can go to the bank on Monday to organise a cheque or direct transfer for the balance of the deposit.
Importantly if you do intend to bid at auction contact the agent and ask them how they would like you to pay the deposit.