Take it to a repair shop
EDIT: Don't listen to that guy, you don't have to waste your time taking it to a repair shop. Simply take an unjamming rod, shove it down the barrel, and the BB should roll out the magwell. If it doesn't, take apart your gun until you have the barrel laying in front of you, then try the unjamming rod again.
Not economically feasible.
Put the Safety on first. Make sure the BB gun is not charged or cocked and unloaded. If the BB is jammed in the barrel you will have to take a .177 cleaning rod and push the BB back into the loading chamber from the front of the barrel.
Leave it to a trained professional
You need to state the model and what is wrong with it.
Send it back to the manufacture or contact the manufacture to find out who repairs your BB gun.
As far as I know Gamo never made a bb gun named the FIX. They did make a model named the CFX, but it is a rifle and shoots pellets, it's not a bb gun. I suggest you contact Gamo at the link below and ask them.
Could be any number of reasons. Jammed. Not loaded, Broken. Time for a new one.
Take the bb gun apart, memorize or take a pic of the inside, find the jam ,and put it back togethor
Cheaper to buy a new one.
how do you fix a front lode washer that is jammed
If its a BB Gun, Then Yes.
Is this a Pellet, BB or airgun? If it's a pellet or BB gun you can use a .177 cleaning rod down the barrel to push the Pellet back out of the barrel into the breech. Make sure the pistol is not cocked. I suggest you look up "air gun repair" on the web and take it to someone who repairs airguns to have it fixed.