How to change pin on android? I have the Blackview BV8000 Pro.

Today, suddenly the pin stopped working and I can not access my phone anymore.

When restarting the Phone (without a sim card), it asks for the pin twice. 
The first time, it tells me it has to know the pin to boot the device;
I enter the pin and the device boots. -> pin is correct.

Then when it gets to the normal login screen, it asks again for the pin - this time it tells me the pin is wrong.

(When a simcard is in my phone, it asks first for the pin - than boots, than asks for the sim pin, confirms that, and then asks again for the pin on the logon screen- which doesnt work anymore.

What can I do to connect to my data?

The PIN is obviously the right one, since my phone can still boot with that one. And friends who know my pin can confirm that its the correct one.
(None of my friends could access my pin in the last few hours).

What can I do? (Besides hard reset it)
Try forgot password and enter your email and password that is connected as play store id they will unlock it and sends the password on your gmail as recovery or as reset it.