Your 2060 is plugged into the motherboard correctly. All it's missing is an 8-pin PCI-E power plug from the PSU.
Most PSUs have them as a 6+2, like this.
View attachment 304299
The reasons why I want you to look at your PSU is because I want to verify it doesn't have any PCI-E connectors, and I want to see if it has enough wattage for the card. If it has no PCI-E connectors but does have enough wattage and you have some other type of spare connectors, can probably get away with just an adapter.
If you need to buy a standard PSU, you will need an adapter like this to convert the 24 pin power into the proprietary 8 pin your motherboard uses.
Buy PSU Main Power 24 Pin to 8 Pin Adapter Cable for Dell OptiPlex Inspiron for $14.99 with Free Shipping Worldwide (In Stock)
www.moddiy.com