How to scale an assembly in one direction?

B. D,

Your zip file doesn't contain any parts, just the assembly file. Use Pack & Go to include all parts & toolbox items.

Cheers

This would depend on how you've created the model and how the height dimension is effecting the other dimensions/design.

You may look into using scale feature and do the scale in one direction only.

You can save assembly as Part file and then scale it in one direction.

File > Save as > Select file type as .sldprt (select Preserve ids option) > Save