We’ve recently bought a car with this feature. Called lane assist on ours, a Hyundai, we discovered we can disable it easily via a button on the steering wheel. If it’s possible on your loan car I’m sure the garage will talk you through it over the phone or if you Google the make and model of the car you may be able to find instructions without needing to phone. Good luck. The feature is certainly disconcerting when it’s not expected.