According to the instructions in the image you posted:
Step 2 is to remove the light cover by releasing the claw with a screwdriver. (See green box & green arrow). That green arrow points to the little, bitty claw that you need to push down to release the catch.
However, your cover does not have the slots in it like the cover in the picture, nor does it have the "Max 5 W" lettering that appears in the picture. Since those slots are to let the heat from an incandescent bulb escape, and you don't have them, it's likely that your fridge has the LED lighting option. The instructions for replacing the LED lighting are highlighted in red in that picture above.
It's likely that only "authorized personnel" are allowed to replace the LEDs because:
- It tells them how often the LEDs actually die
- It allows them to charge for a service call
- It ensures that that the circuit board with drivers, LEDs, etc is replaced properly
- It allows them to recover the circuit board for a postmortem to see how it failed so they can, hopefully, improve the design for future models
- They don't have to supply the circuit board the repair parts supply chain available to the public
Do note: If the fridge is "almost new", Indesit might be willing to replace the light under warranty even though you're not the original purchaser and the warranty might not be transferable. It's certainly worth asking - the part itself is probably cheap, but the service call to replace it probably isn't.
Additionally: I just noticed that there appears to be a slot on the squared edge of the light cover, closest to the on/off switch. I'd imagine that a screwdriver, gently pushed into that slot and gently twisted would pop the cover off.
I also notice that the on/off switch is off. Since it never hurts to double check the obvious: You have turned the switch on, right?