Its a bit of a faff getting WA to work.
You need to grant play services Contacts permission.
Then download what's app from the play store.
Then delete your google account from the device
Then start what's app setup, you will then duringvthe setup log back into your google account. At this point it will find your backup and restore your conversations.
You may need to allow what's app and play services and/ or play store additional permissions... It can be a bit trial and error tho