How do I do this? I've only been able to find one YouTube video on this by a guy who doesn't know what he is doing, so he filmed himself fumbling around blindly and narrating his midadventures.

Do you have the parts you need? That would include the safety lever/s from a P938 (both sides of the safety) as well as the hammer pivot pin from a P938 (it protrudes some on the right side and has a groove to retain the right-side lever in place.

It's been years since I swapped a few (I prefer single side levers on the P938. Back then when the gun was more popular, you could often find someone willing to trade.

I wrote this almost 10 years ago, might be helpful when changing parts on the safety mechanism:

On the P238 / P938, the safety lever is designed to cam the hammer back a little, taking it back so it's not resting on the sear. It does this by engaging a notch on the backside (rear) of the hammer strut. With the hammer now a little further forward due to stoning etc, the safety shaft camming surface it hitting the hammer notch at too abrupt an angle. Checking this should be part of any trigger job where the sear to hammer interface is worked on.

To test: Hammer at full cock, safety off, try to engage safety. Now pull hammer just slightly to the rear and repeat trying to engage safety - easier? You just found the problem.

The fix: (first, don't worry your pretty little head about warranty issues. If your gun up and breaks in half and you are concerned they'll deny your warranty, simply replace any modified parts with stock ones before sending it in. (safety levers and sears are not expensive)

There's two ways t fix the problem, 1) buy a new sear (probably not appealing as there goes your trigger job. 2) Use DyKem or marker to paint the safety lever shaft - operate safety, pulling hammer slightly back further if necessary to get it engaged. Work safety lever several times. This will show you were it's rubbing. Now, using a small file or Popsicle stick with 220 - 320 paper, take down the "approach" portion f the safety lever shaft. Remove and smooth just a small amount. To remain safe, the safety lever MUST cam the hammer back slightly - you should be able to see it move back as the safety lever is engaged.

If too much material is taken off the safety shaft, the failure mode could be that with the safety on, the trigger could be pulled and the sear would be disengaged from the hammer (hammer would still be held by safety lever). Now when the safety is disengaged the hammer would fall. IF the firing pin block safety plunger works as intended, the gun would not discharge - - but it still wouldn't be right.