by tapping "Build Number" 7 times in Settings > About Phone. OEM Unlocking USB Debugging Connect to a PC and use the command fastboot flashing unlock in the terminal.
Since the Realme C30 is not a popular device for custom development (no official LineageOS, TWRP can be tricky due to Unisoc chips), actual available ROMs are rare. However, if you find a hypothetical or ported ROM (e.g., LineageOS, crDroid, Pixel Experience), here are the key features: realme c30 custom rom