How do I stimulate growth on weak areas on a Yew?

I have a Taxus cuspidata that has a couple of weak areas that I need to make stronger but am unsure how to do this.
Is it a case of more sun in that area, heavy feeding etc? I’ve thinned some of the stronger areas hoping that this would help overall.

All input gratefully received,
Regards,
Simon

I attended a workshop on boxwood last weekend with local guru Rodney Clemons. He recommended spraying weak branches with fertilizer. He said this method of foliar feeding works best in the very early morning while the leaf stoma are still open. He suggested doing this once a week.

Maybe this will work with your species.

Frank