3D Model Threaded Hole Modification

I need a prototype 3D model modified to include functional threaded holes that will print accurately. The model is of a multi pipe coupling and should be suitable for ABS plastic printing.

Requirements:
- Modify existing 3D model to add threaded holes
- Ensure holes are functional and print correctly
- Experience with ABS plastic and 3D printing

Ideal Skills and Experience:
- Proficiency in 3D modelling software
- Knowledge of ABS printing characteristics or perhaps other materials if needed.
- Attention to detail and precision in modifications

I am new to cad and am struggling with inventor not actually creating threads, just depicting the threads on the image. Its literally two plates with multiple holes that are threaded. spacing is key so that the john guest fitting screw in. And two thicknesses to allow an o ring to seal the base of the fitting to the base of the fitting on the other plate.
I have someone who can print it, I just need the holes threading properly.