Yes, the black round connector near the cornef of the board.
No additional regulator needed with the adapter you showed. Set it to 7.5V, center positive, and plug it into the board.
Measure Vin.
Connect Vin to your LED anodes, and use suitable resistors between the cathodes and the collector of the transistor.
(~7V - Vf - Vce)/.02 = resistor
ex. (7V - 2v - 0.7V)/.02 = resistor