If the bike is new and purchased from a bike shop, that is on them to fix it and most shops will unless it was oddly sold as is no warranties. However if you are shifting while going up a hill that can cause issues and you want to really back off quite a bit while shifting and be more gentle if you absolutely have to shift up a hill.

If you purchased a bike used, then it would be good to have a good mechanic go over the bike and address any issues going on with it. If the bike was purchased new but from a big box store or an internet non-bicycle retailer than you just need to pay a shop to build the bike and properly tune it. That is something that doesn't happen at a place like that. They may put it together enough for it to look like a bike but they don't properly assemble it which includes tuning it.

Good luck