I have not had to use the converter since I don’t use Minecraft. Looking at the github page the project looks old and not sure if it still works. It appears to work best on Linux and make sure Python is installed. I would try the converter on a copy of a small test world to see how it acts before trying a large world. The instructions on the post appear to be easy but like stated before I have not had a need to use it. I would post questions in the forum on any errors or for more instructions.
How to use Convert Minecraft maps to Minetest worlds ?
https://forum.minetest.net/viewtopic.php?f=12&t=13709
I have not had to use the converter since I don’t use Minecraft. Looking at the github page the project looks old and not sure if it still works. It appears to work best on Linux and make sure Python is installed. I would try the converter on a copy of a small test world to see how it acts before trying a large world. The instructions on the post appear to be easy but like stated before I have not had a need to use it. I would post questions in the forum on any errors or for more instructions.
Sorry I cannot help more on this question.