Welcome to the forum and thanks for your business!
Could you elaborate which „import“ button you’re referring to? If you want to use SVG paths to create shapes, just use the „Open“ toolbar item of the „Add shape“ window.
There is a video tutorial in StitchBuddy‘s knowledge base about importing SVGs.
But if you just want to combine two embroidery designs, open both files and select / copy / paste all stitches or drag from the Finder. There are also related video tutorials.
Edit: For your convenience some links to the mentioned videos: (1.) is rather old (one of the very first tutorials), but still applies, with stitches being selected, copied to the clipboard and pasted into a different design. (2.) is showing a more convenient way by dragging a design from the macOS Finder, which is possible if you want to merge complete designs:
- StitchBuddy - How to combine designs (I really apologize for the awful audio track)
- Merging / Exporting designs with StitchBuddy v2.16
