As Nick says, there really isn't anything you can do by yourself. The transaction fee has to be included when the sender creates the transaction.
There is a provision for transactions to be confirmed without fee, based on a "priority" measure that depends on the size of the transaction, and the length of time since those coins were previously spent. As such, the priority increases over time, so the transaction should eventually be confirmed, though the length of time depends on the size of the transaction. (The size may be larger than the amount due to you, if it includes payments to other people or an amount being returned as "change".) If you have the transaction ID, you can look it up on a block explorer like blockchain.info and see the priority.
If it doesn't confirm in a reasonable length of time, all you can do is take it up with the ATM operator. In principle, they can try to retract an unconfirmed transaction (by double spending) and issue a replacement or a refund.