I assume it's PLA, so you can bake the filament for a couple of hours in a very low oven, about 60C, but do be careful not to reach the glass temperature (Tg) of the filament as this will cause distortion; Tg is around 70C for PLA. Most filaments will recover with this technique but the best cure is storing in a sealed container with a desiccant. Desiccants need to be changed regularly as they become saturated but can be restored by baking; some desiccants change colour when they become ineffective and change back when restored. It is unlikely that this is the cause of your problem and I would first try clearing the nozzle. First heat your hotend to the normal temperature and push filament through by hand, then completely withdraw it. Next, drop the temperature to the minimum for that filament and take a length of filament and push it quickly into the hotend and immediately withdraw it and cut that end off; repeat a few rimes with the fresh piece of filament. What happens is that the cool filament does not have time to fully melt so any contaminants in the hotend stick to the filament and are withdrawn. You can buy cleaning filament that is used in this way. If this does not work check your hotend build, in particular the length of the PTFE tube, because if this is too short you will create a void near the head that will collect soft filament on retraction and will grab the filament as it is fed through, causing a jam.