How do I remove old string out of my CMST920 trimmer if it's stuck?

If you pull hard on this piece it will come out and you can remove it. It is keyed so it can only go back on one way so you may have to turn it a couple of time before it fits. (shown in the first picture) Youneed to press on these 2 tabs to get the cover off if they have not already. (shown in the second picture)