You're looking at an hour's labour for a service on a Zoe so don't pay more than around £100. Shop around and you'll probably get a service for around £70. It's mainly a safety check - they'll inspect things like your tyres, brakes, lights and wiper blades. You'll also get a fresh cabin air filter. Unfortunately it needs doing if you want to keep your warranty, although it doesn't need to be done at a main dealer.