Try this
Check the In-App Audio Settings: Open Discord or BGMI settings, go to Voice / Audio, and look for an option to reset audio settings or manually re-select your input and output device if available.
Replug the Earphones: Unplug your wired earphones and plug them back in firmly. If you use a dongle (Lightning-to-3.5mm or USB-C-to-3.5mm), disconnect the adapter from the phone and reattach it.
Check iOS Microphone Permissions: Go to Settings > Privacy & Security > Microphone, and ensure that both BGMI and Discord have the toggle turned ON.
Restart Your iPhone: A standard system reboot clears temporary audio-routing glitches in iOS.