Here is a step-by-step guide.
You need a custom recovery environment to flash the ROM files. Nokia 2.3 Custom Rom
Installing a custom ROM may void your device's warranty and can potentially brick your device. Proceed at your own risk. Here is a step-by-step guide
If you need a downloadable PDF version or a shorter essay-style version for a blog/XDA post, let me know. This paper is structured as a technical research note. Nokia 2.3 Custom Rom