Q.trimming back zz plant growth
When it grows, do I need to transfer to a larger pot or may I trim it back without harming the plant and how should I trim it back? I have one in a 6″ pot and it is growing.

Yes, you can move the plant up one pot size.
You can also prune back the plant and even propagate cuttings from the plant.
Here are some links with more information.
https://www.gardeningknowhow.com/houseplants/zz-plant/caring-for-zz-plant.htm
https://www.gardeningknowhow.com/houseplants/zz-plant/propagating-zz-plants.htm