As a starting point, the sort of two point interaction you are asking for isn’t the sort of thing you can do on iOS, with Scriptable or anything else (jailbreaking aside). What you need to look to do is wok within what’s on offer from Chamberlain … so let’s begin with what information they offer up online.
I had a quick look on the Chamberlain site and forums and it appears the app doesn’t have a URL scheme to leverage or any inbuilt Siri integration (see below). In fact there seem to be some notes that there’s some base level security built into the app such that you need to interact with the app to work the opener regardless of what typ of interaction you might use.
This discussion on connecting to Siri suggests that what is required is a MyQ Home Bridge. I’m not sure how that fits into your statement about it not working in Europe for Home Kit as that’s what this hardware sees to integrate based on.
Another option might be to interact directly via a web API (Application Programming Interface), but whilst there are a few discussions about roll your own APIs, there’s nothing official, and given that it will require some sort of notable authentication for a security device, I think this might end up being out of reach for you to implement right now. But just in case you, or someone else do fancy a try, these links might be useful. Many of these are integrations with home automation systems, so if you have one of those, then this may provide another avenue to explore.
Sorry it’s not a simple “here’s the solution”, but there’s much more to what you actually want to do than might first have been apparent, and I don’t have any of the kit (including a garage) to figure and test it out with. Hopefully there’s something here though that will help.