Open the lid that hides the pressure sensor.
That usually does the trick.

OTOH, Android One might be a better option.

Don't count on it. I for one have given up on BlackView. A shame, really.
I totally digged by BV6000.

And I still get "you're up-to-date" though I'm on 20170708 ...

Needless to say, flashing does NOT work either

They will never deliver, which is a shame as the BV6000 is a great phone.
Personally, I've given up and moved on to another manufacturer who IS supporting even older hardware.

@Asier99
Did you check all the other "update" related threads in here?
TL;DR -> no

When will you provide a link to the 20180515 ROM? never Why? :? Because we heard "they will come (soon)" for such a long time, it's getting ridiculous. Given the fact that BV probably isn't making much money off their phones, from their POV it makes more sense to focus on supporting newer...

Yea, and OTA doesn't work properly either. Great.
So, basically, if you have 20170708 installed, you are stuck.

*sigh* I don't even get OTA offered and flashing doesn't work either...
So I'm stuck at 20170708 and security from May 2017.

I still totally dig my BV6000, but BlackView's update... policy is, frankly, crap. Big time.

That's Marketing Speak for: Not bloody likely.