Forgotten pin so cant factory reset

Not used my tablet in ages and fotgotten the pin code.

Need to do a factory reset but it wont power off without the pin.

Tried holding the power and volume button but it just restarts and doesnt take me to the menu to let me choose the factory reset.

Followed god knows how many online videos last night and got no where.

Do i need to wait for the battery to die to be able to do this pricess now?