I want to add an additional USD socket somewhere on the dash to charge my Lenovo tablet without trailing cables
Any advice on where I can fit it and how do I connect the wiring?

I use a QC3 plug which pushes onto the standard power socket. It doesn't even stick out, which it just perfect for my use. Much less work than wiring in something aftermarket too. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Yea, I too

https://www.ebay.co.uk/itm/363988296792?ch...0686380774

I use one that's more discreet than that, fitting inside the power socket, but it only has USB A and USB C with QC3.0 sockets, but that's enough for my use.

https://www.ebay.co.uk/itm/144559629676?mk...media=COPY Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

I've had trouble with those adapters getting a consistently good connection in the cig lighter power sockets. If it was my daily driver I'd disassemble the shifter console and hardwire in a USB port. Maybe replace the rear power socket.