Many hobbies are when people collect a lot of items. It could be say, dolls. Now if you worshipping these dolls yes its idolatry.
When people start collecting, they covet what they havent got already. It starts to consume them and they become addicted to always having more. This takes them away from God because the time spent on their hobby is time taken away from God...and He is not pleased with any sort of idols before Him.
What can you do, well you can repent of this idolatry and coveting.
There are hobbies or pastimes you can enjoy that dont mean you have to amass huge collections of stuff so that you become a hoarder, but you must give glory to God first.
In the bible book of Acts there was a lot of idolatry in Ephesus where people had their livlihood making statues of the goddess diana. The more statues you had perhaps the better 'luck' you had. Also it was making a lot of money for the craftspeople. This is like when people collect 'art' these days and often this art does nothing to glorify God. Maybe people collect it to show off how rich they are.