Remove the hot end, it’s pretty easy, just watch out for the connectors when you disconnect them, they’re marginally too easy to pull off if you haven’t cleaned all the silicon goop off. Then take the cheap 1.5mm Allen Key that came with the machine, hold it with some pliers and heat the end up good and hot with a lighter. Then, jam the heated end in to the top of the extruder, impaling the stump of filament that’s there. Wait a minute for things to cool down and then pull hard and the key should extract the stump and also deliver you a “cold pull” removing particulate with the hardened filament. Much easier than almost anything else you could do. Works great. If the filament doesn’t pull free, you didn’t get your Allen Key hot enough/deep enough. Try again.
Then, reserve this Allen Key for filament pulls and buy a decent tool to replace it, that won’t round off on you after the third or fourth screw you’ve tightened.