Hello! My child has screwed up the rear seat in my Honda crv. Are there any ideas where I can look to buy another one from used car in Switzerland? Would appreciate for any advises.

Go to a car wreckers - called Autoverwertung here in Switzerland.

Know what you want before you go, and be armed with
a) Car Make, model and year
b) New price of the item you want to buy (for comparison purposes)