Tinkle tinkle not
You need to have at least 1000 pairs of byakugan and being an oststsuki member first
Get SP to write a filler love story about from blind puppet master fro the moon, who steals you little sister eys, and transform them into the Fillergan.
1000 byakugan was needed to power the tenseigan machine, tenseigan (the eyes) is needed to control the machine. You awaken tenseigan by implanting the byakugan into an Otsuktsuki member from Hamura's lineage.
It's similar to how the rinnegan was awakened, except you don't need to be a transmigrant, you just need to blood of the main branch. Toneri was from the main Otsutsuki lineage like Madara and Hashirama was from Hagoromo's lineage and Hanabi was from the main branch of the Hyuga.
EDIT: I suspect that the reason the power of a transmigrant is needed for the rinnegan to awaken, is because the power was diluted after every generation, while the Otsutsuki and Hyuga remained pure, however the branch clans have their eye power sealed.
Call it filler all you want, but at the end of the day Kishi can choose to include it in future events if he wants to and expand on it's power if he wanted to. The reason the Hyuga hasn't been developed was because the whole of Naruto was all about Hagaromo's lineage. Now that it has been dealt with, Kishi has stepped into the Otsutsuki territory and the Hyuga is the closest to them with their Byakugan. I don't believe Kishi will just end things with this movie, because there is still a lot of unanswered questions and Kaguya's enemies still hasn't been revealed. The new hero is also part of the Hyuga lineage.
EDIT: I see some people call Himawari awakening Byakugan a retcon. They forgot how the sharingan originated. The original sharingan couldn't be deactivated either and the sharingan the Uchiha inherited came from Hagoromo's rinnegan, another dojutsu that couldn't be deactivated. How can you call it a retcon when something similar happened with the sharingan? Add in Hagoromo's yang chakra and you are bound to find a new type of power than just Hamura's.