Hi Waltecar, A groundsman or greenkeeper would find this a relativly easy patch and repair job but it's not that tricky if you want to give it a go.
2' x3' is not too big to try this :- Cut three sides of the area at right angles to each other with a spade ot edging iron approx 3" deep, you could use a board to keep it straight, make it a little bigger than the dip.
Now you need to roll the turf back like it's a piece of carpet but to do this you have to cut through the roots of the grass.
Decide which way you want to roll it back (like a swiss roll) and bagin carefully to push down with your spade, 2"-2.1/2" and start to leaver it back until you can flap it back and then continue cutting horizontally by using a sliding action with the spade.
A good lawn should hold together pretty well.
Next thing to do now is investigate the uncovered area to see if there are any old tree roots etc, the could be causing the ground to sink and if so, it will need digging out.
Now add some top soil to the dip, perhaps with a little compost mixed in to give the roots a good start.
Use you own judgement on how much to fill then firm it down well, then roll the turf back then firm down the turf by standing on the board. If you have got it right first time, you should be able to lay a piece of wood across it and have No gaps under neath.
All you've got to do now is keep it watered well til it gets growing again. Good luck. Tbird+