I think you only need to unzip the iso version with an “unzip” soft (try the free version of WinZip). You’ll then retrieve the m2ts file (there are several, just open the biggest one and check if if contains as it should the movie file) that you can mux as mkv with mkvtoolnix (the size will decrease, which is normal since m2ts use redundancy space, which is needed when you read the file burnt on a disc but which gets removed - because useless - when contained into mkv files).
This is not that hard, it might be the very first thing I’ve learnt when I joined this forum 😉
Let us know if you need more help.
Cheers once again, Malá! 😃