xnview[.]com/
MobiKin HEIC to JPG Converter is the GOTD, & it's probably fine for what it is -- I have zero Apple products, so no way to say yea or nay regarding the software. And if I did have to deal with HEIC files, rather than installing another app, I'd open XnViewMP, a really useful utility for working with photos/images.
XnView is free for non-commercial use, has portable versions available, is frequently updated, and the MP version I use is sort of the swiss army knife of utilities for working with photos. It'll open 500 image file formats, export 70, and has some features that can be pretty hard to find, like *lossless* jpg rotate & crop.