How to put together splitted stl model parts

Lets say I have stl model that was already separated into multiple parts.I.e. the model designed to be 3d printed separately part by part and then to be put and glued together manually.
For my own reasons I would prefer to print the model as whole part rather then separately. The problem is when I import multiple stl files into blender then are not connected inside a Blender.I tried to put all parts together inside Blender by dragging them inside each other but it is close to impossible task.
So my question is there any quick and dirty way to somehow automatically joint all parts within Blender ?

Thank you.

If you want to do it in Blender, I’d recommend using object snapping set to vertex or face.

I’d also try opening the parts in Meshmixer too, if Blender is being less than helpful.

Try Edit mode: Mesh → Merge → by Distance (choose Distance), Select → Select All by Trait → Interior Faces , delete.