How do I convert HEIC format to jpeg?

You can do that by exporting the file as an "edited" file with these options:

The key here is to pick JPEG. The other settings are as you see fit.

Select the photo an go to the File ➙ Export ➙ Export 1 Photo… menu option.

Hi

Select the image thumbnail, or multiple thumbnails if you want to export more than one.

File menu>export