Continue to learn, gain assistance when needed, and know what you don't know.
No one expects you to do it all, or all by yourself. That's why there are so many careers out there. If you don't know something about your business ask yourself if it's something that is better off outsourced. If so, then do it! Solicit the skills of an expert in that field so you can continue to be the expert in yours.
If the gap requires an education - get it! Learn the things you need to in order to continue to be successful.
And don't hesitate to enlist the services of a coach to provide you with some of the things you may need. Those things can be: training, mentoring, accountability, structure - to name just a few.
Just remember that you don't have to struggle to gain knowledge or develop skills.