Adding a new graphics card to my Inspiron 3910

Hi.

I have an Inspiron 3910 (Service Tag - ***private info removed) and I've had no problems at all since purchasing it a few years ago.

At the moment, I'm trying to install the following graphics card which has been difficult to register on the PC:

   - Dell Nvidia GeForce GTX 1660 Super 6GB GDDR6 Graphics Card

The Dell website claims that it's a compatible graphics card. It fits cleanly in my PC but I'm getting the following message at the moment when plugging the HDMI cable into the newly installed graphics card:

   - Please power down and connect the PCIE power cables for all graphics cards

The graphics card seems to fit perfectly fine and I've got no issue with the fitting into the machine.

I can see that there is a 6 pin connector with one small square pin connector plugin for the graphics card but the same shaped pin doesn't seem to be available for the integrated graphics card.

Can someone provide me with a solution to this please?

I have very limited knowledge with software and your help would be greatly appreciated.