Look in the reference section for one of TooSixy's P30 disassembly/trigger replacement guides -- you'll find a picture of the trigger return spring in one of the guides.
You really shouldn't need a picture. Look down into the area above the trigger, where you'll find a small spring coiled around the trigger pivot axle. One leg of the spring extends forward, on the right side of that area, in line with where the slide stop's cross-pin passes through the frame. Grab something like a dental pick and lift up on the spring leg far enough for the cross-pin to pass under the leg. Release the leg so it falls on the cross-pin, and verify the end of the leg settled in the spring leg notch in the cross-pin.