As a 6th dan black belt, I'm sure you know how to punch/kick.

Just plan out what you're gonna do!

ie:

You and your partner is running towards each other.

When you're a few feet away, it's time to plan on what to do.
Say you want to kick him.
"I will kick you, can you dodge/block?"

Do the kick, try to miss or something. Do NOT push your partner away if the kick hits, relaxing knee/hips when the kick connects helps.

Try to stabilize by going in to a horse-stance or whatever looks good after every encounter, and plan anew again!

I'd suggest you go and just find another person to spar with.

It'll come naturally!

Good luck!