It helps to have a home made armorer’s block.
Start with the trigger bar engaged with the trigger, keep your left thumb on that end, and place the end where the trigger spring engages the trigger bar with that part BEHIND the sear housing.
Engage trigger return spring in that end like so.
Take your left index finger and engage the trigger return spring to that part.
Push the trigger bar around the sear housing while maintaining left thumb pressure on the trigger/trigger bar part and it should pop right into place.