Hi, and Welcome Bro.
As mentioned previously, a tear down might very well be the best way to find what's causing your volume button to stick. If this is not possible for your, you might still be able to fix the issue so long as what's causing the key to stick is some kind of loose debris and not some kind of sticky gunk (i.e. - syrup, juice, etc.). Simply acquire some canned air and try blowing through the included straw nozzle into the tiny gap around the key. Make sure you shake the can thoroughly though, you don't want any moisture going in with the pressurized air and risk setting off the Liquid Damage Indicator inside, as that will void your warranty.
Speaking of which, most devices come with a one year warranty that is usually covered by either your manufacturer or your service provider. If the above options are not possible for you/fail to solve the issue, you can always either call them and inquire as to either what repair services or replacement options they can offer you. In my experience, Samsung in particular is pretty good when it comes to device repairs so long as it's still within the warranty period and the device is in otherwise good condition.