I believe I found the answer, you must go to
In media settings tab:
Set media preferences
HD Video Resolution
There is a 'button' to enable HD content. Switch that on.
Solution found on a Reddit entitled: "HD video and 10GB 4G Tethering NOT enabled by default (for One Plus Promo / Verizon matching) "
That's the exact instruction set we would have provided.
I have the T-Mobile One International plan on only my line amongst 3 other numbers on the plan and I am still unable to stream HD video over LTE on my phone or tethering...
I also don’t see the media settings option on T-Mobile.com or the iOS app. I found the exact url on another thread ( https://my.t-mobile.com/profile/media_settings
The media settings state that my line is not eligible for media settings even though I have the T-Mobile One International plan...