Here's another easy way to reassemble the Krag trigger unit:

Use a #35 drill shank/.110" diameter (or a 7/64" drill) as a 'guide pin'.

Put the sear spring in its hole at the front of the sear and start the 'pivot' on the front of the sear into its hole in the receiver.

Open a 1903 Springfield tool into an "L" shape.

Place the Krag action on a table or bench, (left-side 'up'). With your left hand, hold the heavier leg of the Springfield tool against the end of the sear spring. The narrower leg of the tool should point toward the left.

Grasp the rifle's trigger with your right hand while turning the tool counter-clockwise. The tool will ride down the incline of the receiver compressing the spring. Wiggle the trigger/sear until it moves downward slightly partially catching the coil spring on the rear flat on the receiver. Once the end of the spring catches on the flat, the trigger can be pushed forward and then downward so the sear is fully seated.
(As Local Boy indicated, the orientation of the sear-spring is important. Sideward movement of the trigger-assembly is easier, if a smooth beveled area of the coiled spring engages the edge of the receiver).

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