A bit confused, how does Keppel Corp breaking out of a base formation at $4.60, indicating an upside of at least $5, help the STI which is at 2.69 today?

Keppel Corp makes up 3.3% of the STI. This means that if everything else doens't move and Keppel Corp is up 10%, the STI should theoretically move 3.3% * 10% which means the STI will move up 0.33% if everything else doesn't move.

Also, not entirely related to Keppel Corp, but you should not be investing money that you need in the short term as the market can experience significant short term volatility.