Remove the crank and secure in a vise. The procedure can be done with the crank on the bike but it’s easier if it can be held still.
Attach the appropriate reaming tap to the tap handle. Use 1695.1AL for the left arm, 1695.1AR for the right arm.
With a generous amount of cutting oil (it can be done dry but that wears the tool faster) ream the pedal bore until the thread cutting section of the tap starts to bite
Still applying more cutting oil, cut threads through the entirety of the bore
Remove the tool and clean/degrease the newly cut threads
Spin the appropriate insert onto a new pedal. 1695.4A for the left crank, 1695.3A for the right.
Apply red Loctite to the external threads of the insert. You can apply it to the threads you just cut in the crank if you prefer.
Using the pedal as an installation tool, spin the insert into the newly cut threads.
Let the Loctite cure for 24 hours.
Carefully spin the cranks to make sure any insert that is projecting beyond the backside of the crank won’t make contact with the frame or any other part of the bike. If it does it can be filed down to make room.