I only buy DVDs which are in English or have built-in English subtitles. So I'm no expert on this!
Try first to access the opensubtitle.org website on a computer (not the HiMedia box!)
I just visited https://opensubtitle.org on my desktop.
(It was definitely down when I checked last week, but is working now)
You can also try out the beta site at https://www.opensubtitles.com/en
I did NOT need to register.
I did NOT need an account.
I did NOT add any extensions to my browser.
I just picked on some movies at random and downloaded the subtitle files for them.
No problems

!
Then just copy the srt files into the same folder as the movie.
Just went to https://www.podnapisi.net/
That works also

!