Very high risk of bricking

You will almost certainly destroy the board.

Heat guns are not reflow stations. They blast hot air over a wide area, heating nearby components—caps, resistors, the CPU socket—way past their tolerance. Soldered RAM (BGA packages) needs precise, controlled temperature curves. A heat gun gives you a blunt hammer when you need a scalpel.

Even with a proper hot air rework station, replacing BGA RAM is risky. You have to align the new chip perfectly, apply the right solder paste, and avoid overheating the surrounding area. One slip and you lift pads, pop nearby caps, or delaminate the PCB.

I’ve seen people try this with a heat gun on old laptops. The RAM might come loose, but the board usually doesn’t boot again—either the RAM was never fully reflowed, or something else got cooked.

If the RAM is soldered and dead, it’s almost always cheaper to buy a new motherboard or a different laptop than to attempt this. The board is worth more than the gamble.

Leave this to someone with a proper rework station and experience. Future You will thank you.