Depending on what the problem is, they can but may need to send out for repairs. Make an appointment before going in.
Apple definitely does offer device replacements for Apple Watches, but that entails a device replacement in most cases (even if you are only charged for a battery or display). Before going in for service you'll want to schedule an appointment and review pricing :: - https://www.apple.com/retail/geniusbar/ - https://support.apple.com/watch/repair/service/pricing
Thanks! Your answer is awaiting moderation.