I have a TDR 125. Used to have similar flooding problems. Don't know about the DTR but on the TDR there's a little screw on the bottom of the carb. You'll know it cause there'll be a little tube running out and the screw basically closes off the tap at the top of that screw.
Finding the carb might be tricky if you're a total noob, I know it was for me! Just think of it this way, air and fuel go into the engine and the amount of fuel is controlled by the throttle so find the block of metal that links the air box, engine and probably the throttle cable too. Your little tap screw should be at the bottom of that.
Now, when you're opening a screw that's probably rarely opened and is often exposed to the elements you'll find it tough... then your screwdriver will slip, you'll strip it and you're... eh, begins with f, ends with ucked. But worry not, all you need is WD40 before you start, wait a few minutes, put the screw driver in place then whack it with a hammer. Put as much weight as you can down the shaft of the screw driver so you don't slip and it should turn with a little crack then almost no effort.
DO NOT over tighten when you're doing it back up.
Finally, chuck your plug and put in a good one. I have to replace the plug on mine about every 1500 miles. 2 strokes just don't like civilized city driving and get fouled up unless you drive them frequently within 1000 rpm of the redline.
Enjoy thrashing her about when you get her running again, they're great fun little bikes