How to create a local fine mesh on a synthetic volume

Greetings to all

I’m a beginner with Cubit. I’m trying to mesh a cubic synthetic volume consisting of 27 grains using cubit. The model includes the surfaces of the grains, and the grains imported as .stl files that I created using Dream3D. I wish to use this model for nanoindentation process. I want to create a fine mesh under the indenter tip while the rest of the cube has course mesh. I’m not sure how to do this local fine mesh on my model.
Please share with me anything that can help.

Thanks