Ok a little more progress
i have found two apps that don’t require Root that will re map the hardware buttons one called button remapper and the other called button mapper.
the better one is button mapper as it will allow you to assign an app ( phone dialer in my case ) to a double press rather than a short or long press which gives a third option for the back button
once button mapper is set up it works from the clock face screen and then i can use ok google to dial the number i desire
but it only works once
once i leave the dialer the app seems to lose it’s permissions and deactivate
i can open the app re activate permissions the app and it works again but once only
i have no idea whats deactivating the permissions which in turn disables the app if anybody could shed some light on this i would be grateful