It's just an EXR file. Run Blender with administrator privileges and you should find the file (once you unpack it) in C:\Program Files\Blender Foundation\Blender 2.91\textures :-)
If you copy the file out somewhere just rename as .exr
Many free photo editing apps like Krita can open this file and save in another format like TGA if you prefer.
Please also note that the maker of ANT landscape also makes the TXA landscape (includes procedural texturing) - https://github.com/nerk987/txa_ant
and I just checked - this tip only seems to work with TXA
Watch video Blender tip - export heightmaps from TXA (replaced ANT) Landscape addon online without registration, duration hours minute second in high quality. This video was added by user DavRenders 06 January 2021, don't forget to share it with your friends and acquaintances, it has been viewed on our site 443 once and liked it 6 people.