This video is a good resource if you want to try front derailleur adjustment yourself:
First thing is to assess where the chain drops. In the extreme positions (largest chainring/smallest chainring), the side plate of the derailleur should not allow the chain to move over the chainring and drop but also shouldn't touch it when you shift on the highest gear on the back (smallest cog rear vs large chainring at the front respectively vice versa).
If there is too much of a gap, the corresponding adjustment screw on the derailleur needs to be moved, the derailleur should move visually on a quarter of a turn, so watch out how it reacts and only make small increments before you try shifting, again.
Based on your comment above, if the chain drops shifting on the middle, the derailleur is probably not adjusted properly (cable tension too low), the chain will try to jump on the middle chainring, but if it isn't able to move far enough, it will fall off and it is very likely that it just bounces/drops instead of going back on the smallest chainring -> this calls for indexing as suggested in the video.
Ideally, you have a work stand so that you don't have ride around or flip the bike to verify if your change made an impact.
Needless to say: If the bike is new from a shop and left it like that, you have every right for them to fix this at no charge.