Can't re-enable permissions for OTA Android Upgrade

Hi all,

Got a problem of my own making I need some help sorting out

A while back I inadvertently denied permissions for the OTA update to access my phone... I think it was when the box pops up asking for permission to access SMS, phone etc.

I had only intended to delay the update till later but accidentally selected 'Don't ask me again' and now I can't seem to update Android on the device. Selecting a manual update through 'About this phone' causes the confirmation screen to pop up for half a second before disappearing again. How do I re-enable permissions for the OS update?

I'm on a Vodafone Smart Prime 7 and Android 6.01.

Thanks in advance