Getting the trigger group back in is easy.
Take a deep breath and relax (no insult intended) and look at the parts.
1) Insert the trigger and sear first, aligning them with the middle hole. The trigger and sear go in together and will be under some spring pressure as you will have a small spring and plunger that fits between the sear and trigger. You will have to press them together and hold them (there will be noticeable spring tension) aligned with the hole and tap the pin in from the side. All pins insert from the left side. This may seem to require six arms, but it really isn't hard.
2) Once that's in, slide the hammer in and pin it into place.
3) Once that is done, you will need to insert the keeper, which has a hole and two notches. The notched end, with a flange, goes under the hammer pin on the right side. Position it so that the notch is over the pin and the keeper is pointed forward. The flange will be to the left. Hook the notch around the pin and then rotate the keeper to the rear, so that the second notch engages the sear pin. Align the hole in the keeper with the rear hole.
4) Slide the selector switch into the lower receiver so that it retains the keeper (have the selector switch lever pointed up). Rotate the switch to "safe". Now the assembly is in there.
5) Take the hammer spring assembly and insert the knobbed end into the recess on the hammer on the right side. This will leave the plunger cap pointing to the rear (it will look like a witness punch pointing towards the rear, with the plunger and spring inside the cap and the knobbed head inside the notch on the hammer). Push the plunger hard towards the hammer while also pressing downwards until it slips into the small notch just above the selector shaft. Be careful as it will be under a lot of tension.
And that is that.
Ash