You buy a suspension-less, road-going hybrid commuter e-bike "mostly for off road hiking around the forests"? Yeah, right!
The Impel range is too new. More, the Hyena electrical system it uses is too new, being totally different from anything Halfords or AFAIK any other maker has used before.
Halfords have been pretty clever at foxing those wanting to crack speed limits in the past. Having glanced through the Impel Manual, my guess is they've been even cleverer with this new system.
If you want to give it a try, you can try holding down two or more buttons together for a few seconds and see if any Program Menu's pop up on screen. Or else there may be something in the Bluetooth app, but unlikely IMHO.
In the past with Halfords usual Suntour systems, owners have resorted to upgrading almost all the electrics for extra speed (among other reasons).