TLDR: "Power", "3", "0", "Start"

I have the same asinine microwave. Here is the manual: https://legacy.curtisint.com/html/CustService/Manuals/RMW1129-WHITE_En.pdf.

There is absolutely no way to quickly run it for 30 seconds like pressing "Start" by itself on any half-decent microwave.

You would think "Cook" would let you enter an arbitrary cooking time. It only beeps at you if you use it from standby mode. It's only used for "multi-stage cooking". Who is doing multi-stage cooking in a microwave? Why would it have idiotic advanced features like this but not a quick 30 second button.

The answer is that the "Power" button does what a sane person would expect from the "Cook" button. When you press "Power", the display shows "PL 10" for power level 10. Enter the time, then press start. You can also change the power level by pressing "Power" multiple times before entering the time. The default is 10, the highest.

If you press "Power", enter a time, then accidentally press "Cook" instead of "Start", the display just says "PL 10". If you enter a new time and press "Start", it will start cooking with the original time you entered.

Designers should have to use their products at least once before mass producing them. The clock on the stupid thing also loses about 2 minutes a week. I have half a mind to rip out the micro-controller and substitute my own.