How to know whether my transaction is fraudlent after one confirmation? Let's say if the transaction tx_1 has one confirmation. But the tx_1 is fraudulent. Can it be rolled back? Here I am storing the confirmed blocks and if my transaction is in the block-1 then the confirmation of tx_1 is 1 and whenever the blocks come after the block-1 the confirmation will keep on incrementing. But after one confirmation, if the tx_1 is fraudulent then how to stop that transaction?
You cannot undo a confirmed transaction trivially. That is one of the key benefits of a network like Bitcoin.

If your tx has only 1 confirmation, you might yet be able to drop it by mining two blocks on the parent of the block that contains tx_1. However, this requires you to have enough hashpower to be able to do so before someone extends the chain building on the block containing tx_1, which is non-trivial. Additionally, even if you succeed in this, there is still a chance that someone might mine on the block you dropped and turn that into the longer chain again.

Usually, blocks which have been confirmed 6 times are considered irreversible. Practically, unless you have access to a large amount of hashpower, even 1 confirmation is effectively irreversible on the bitcoin chain (although orphan blocks do occasionally happen)