If the freezer seems fine but the fridge has gone warm then the fault will be in the freezer. As the fridge section gets its cooling from the freezer section.
What you need to do is either empty the freezer and from there remove the back panel.
Once thats off you will see another plastic panel, Remove this as well.
Behind there you will see the evaporator. Check to see if theres an ice build up behind there. If so then use a hairdyer and melt all the ice from there.
Once clear refit the panels and retry the appliance and you will find the fridge section should get up and running again from there.
Or another option is a full defrost of the appliance. Empty it and unplug it for 24 hours and leave the freezer door open. This will allow the ice behind the panel in there to melt itself.
Then see how it goes from there. Fingers crossed its a one off that caused this but if it happens again then its possibley a fault on the defrost side of the appliance.
Try the above and see how it goes from there. If you need anymore info just get back to me.
The back panel i said to move is inside the freezer itself not at the back of the appliance.
You need to empty the freezer and then inside the freezer itself at the back thats the panels you need to remove to access the evaporator unit.
If you get stuck just get back to me again
Not the esayist things to move are they.
Check behind that panel inside the freezer and im sure you will find thats blocked with ice.