If you do not have ADB access from another device, you must do this manually: Power off the device, then hold (varies by manufacturer) until the Fastboot screen appears.
Note: Running Fastboot commands from the phone to the phone is heavily hardware-dependent (often requiring a special cable or another device). However, assuming you have the android-tools installed in Termux and are interfacing with the device (perhaps via an OTG setup or debugging bridge), the command syntax remains the standard protocol.
Verify the connection in this mode by typing: fastboot devices Step 5: The Unlock Commands
Upon confirmation, the device will immediately format the /data and /cache partitions. This is a security feature. If a thief steals your phone and unlocks it, they should not have access to your personal photos or files. Everything—your settings, apps, photos—will be erased.
Once you send the command, Device B will display a warning screen. Use the to highlight "Yes" or "Unlock Bootloader" and the Power Button to confirm.
To unlock a bootloader using Termux, you cannot do it on the same device you are trying to unlock. You need a "host" setup: Device A (Host): The phone running Termux. Device B (Target): The phone you want to unlock. OTG Cable/Adapter: To connect the two phones.