I want to perform a collision attack
Actually, the problem you cited is not a collision attack, but a second preimage attack.
In a collision attack, the attacker gets to select both messages; as long as they are distinct and hash to the same value, the attacker wins.
In a second preimage attack, the attacker is given one message, and is asked to find another message that hashes to the same value; if he can, he wins.
You have already specified one of the messages "s3412347"; the only flexibility the attacker is allowed is in the second message. Hence, this falls under "second preimage attack".
Here's why the distinction is important: for SHA-1, there are knowns ways to do collision attacks (which require rather more computational effort than what a student is likely able to get his hands on, and certainly not something you can find online for free); however there are no known feasible ways to do second preimage attacks.