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!