If you are having difficulty changing your riving knife, usually, there could be usually 2 scenarios.
One scenario could be that the Riving Knife Locking Pin is not unlocked or properly unlocked causing the riving knife to not be able to get out of position, or it could be that the bolts of the riving knife holders are tightened too much.
If you are having trouble replacing the riving knives and the issue is not from the Locking Pin, please try using an allen wrench to loosen the larger bolt that is in the center. Please refer to the below image for guidance. If the issue is from bolt being too tight, by loosening this bolt slightly, it can help make switching out your riving knife easier.