Use a Phillips screwdriver to remove the screws holding the air box cover in place near the tool's carburetor. Insert the screwdriver into the screws and turn it left to take them out. Set the screws and the air box cover aside.
Pull the old primer bulb out with your fingers or a pair of needle-nose pliers and insert the new one on the primer base.
Set the air box cover into position and tighten it down with its retaining screws using the screwdriver.
Open the gas tank on your Ryobi tool and empty out the old fuel mixture.
Pull the fuel line off the end of the carburetor.
Cut the base of the fuel line underneath the gas tank with a pocketknife or scissors and use the tip of the screwdriver to push it up into the empty tank.
Hook the new line to the line installation tool and then feed the line down into the gas tank. Pull the fuel line through the hole at the bottom of the tank until it snaps into place.
Slip the other end of the fuel line onto the end of the carburetor.