Awareness of imposter feelings when they emerge is the first step. Track these thoughts, what they are and when they occur.
Remind yourself it's normal not to know everything and that you will learn more as you progress. Rewrite this in to your mental programs.
Others may feel the same as you, so open a dialogue rather than harbouring your negative thoughts alone.
Self-doubt can be a normal reaction when you are out of your depth. Just because you feel a certain way at one point in time, doesn't mean that's the way it always is, or should be. Consider the context.