IMO, the way I would go would be to pull both the barrel and the breechblock, and remove the mainspring & it's strut, to reset the hammer into the half-cock notch.
Be sure to remove the axles toward the right side of the rifle as the sights are viewed for firing.
Then, the breechblock can be re-installed, first easting the forward tip of the mainspring strut in it's seating slot in the bottom rear face of the breechblock simultainousl with seating the plunger/cone-shaped end into it's seat in the lower hammer face.
Re-install the barrel last.