To reset your micro:bit to run the default program that came with it (called the Out Of Box experience), download and flash the .hex file from the microbit.org page about the Out Of Box Experience. If you are unsure on how to do this, follow our article on How to transfer code onto the micro:bit via USB.
The Out Of Box Experience (OOB) runs through a demonstration of all the features onboard the micro:bit. On the latest micro:bit V2 this includes the speaker and microphone and on all micro:bits V1 and V2; the LED display, A and B buttons, Accelerometer and Compass. There is also a hidden Easter Egg that you can unlock by pressing A+B when you see the heart animation.
The code for this OOB experience is written in C++, it will therefore not load in the MakeCode or Python Editors. We hope to make versions for these editors available in future.
The original source code for the OOB experience, was provided by our friends at Technology Will Save Us and has since been developed and released by the Foundation (source code for micro:bit V1, and for micro:bit V2).
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