How can I access data on Charge Only mode (Phone's screen is non-functional!)? I have a Xiaomi Redmi Note 3. The phone was accidentally dipped into the water which rendered it unusable. I left the phone to dry in a rice bag for 5 days and then took it out and charged it.

The phone booted and was working until I put it to charge. The moment I switched on the power adapter, the screen went black and then the backlight came on.

I remember that before the incident, the phone was in charge-only mode and as the screen is non-functional, I cannot change the mode now. I was wondering, if there is any way, I could access, and recover my data before I give it to any authorized Service Center personnel, who says that there is no chance that the motherboard is fine.
There's little chance you can do that in normal system. But you can do it in (custom) recovery.

If you already have a custom recovery flashed, then skip this step. Boot it into fastboot (bootloader) and flash a custom recovery in.

Then boot into the recovery and you can access it using ADB shell. You can use adb pull to retrieve data from your phone.