This instructable is not recommended for novices. You should have a fair amount of technical confidence before opening and modifying your Tello drone.

Having said that; This is a great way to gain a fair amount of technical confidence ;)

So you want the front camera on your TELLO drone to point downwards?

Maybe you want to make cool birds-eye-view selfies?

Or maybe want to be able to do machine vision based navigation?

Perhaps you want to try try programming the Tello with the experimental TelloStorms block programming software which is part of a masters' thesis at the Department of Computer Science at Aarhus University?

Either way, here's how to do it..

REMEMBER: REMOVE THE BATTERY BEFORE DOING ANY OF THESE STEPS!

You'll need:

A Small phillips screwdriver: PH000
A flushcutter/wirecutter... (A pair of really sharp scissors might do, nailclippers could too..)
A Hot glue gun, or some sugru, (or maybe just sticky-tac, or a paper-clip.. i don't know.. improvise)

Step 1: Open Up

REMOVE THE BATTERY BEFORE DOING ANY OF THESE STEPS!

-Use a small phillips head (PH000) screwdriver to remove the 4 screws that hold the bottom cover in place

-Pull the cover off.

Step 2: Lift...

Use something that wont cut/damage the circuit board (i'm using a zip-tie) to genly lift it at the back.
Pull it genlty backwards to reveal the front camera housing area.

Step 3: Pick...

Pick out the rubber part, and any other loose plastic, like the nifty optical fiber plastic thing, that leads the light from the motherboard to the front of the drone :)

Step 4: Unscrew

Unscrew the two screws holding the camera mount.

Step 5: The Tricky Part...

Lift an the camera mount out of the Tello. Don't twist the cable too much, don't force anything too hard. Just be careful. The LED light optical guide might come out too, don't worry too much about it, it's just a fancy piece of plastic that makes sure the status light looks nice.
Slide/set the circuit board back into place.
If you want to be able to revert back to a fully virgin TELLO, find some way to mount the camera without removing any plastics, like this guy here: https://tellopilots.com/threads/ryze-tello-camera...

Step 6: Optimisation.

To make the camera smaller, cut off the plastic mounting bits.

Step 7: Snip Snip.

Clip the little plastic bit that would otherwise poke at the camera flat cable when the bottom cover comes back on the TELLO

Step 8: Close It Up.

Put the bottom cover back on. Fasten the screws. You should have two left over, these are only needed i you ever want to revert this hack.

Step 9: Fixation

Use a bit of hot glue to fixate the camera in the desired direction.
Power on the drone and observe the camera feed while doing final adjustments before the glue cools down completely. Hold the drone level and directly above an easy target, for added precision.