If there isn’t a BA at the derailer, there should be one at the shifter. Failing that, there should be an inline adjuster smack in the middle of the cable casing somewhere.
I can’t imagine a bike like that sold w/o adjustment ability.
If you know what a barrel adjuster looks like, you should be able to find it. They all work pretty much the same anyhow. Once You’ve found your BA, proceed according to the videos.