ZANUSSI ZENB9750SI (92840523100) FRIDGE NOT WORKING?

Fridge is no longer cooling. This is the second time this has happened in 2 years. Last time, technician came round and replaced what looked like sensors. They look like NTC probes. Want to try and fix this myself now.

I noticed if I look in the freezer compartment through the vents at the top there is a lot of ice on the left side.

Any ideas on what could be wrong this time round?