Disclaimer: This project involves high voltages. If you are not comfortable working with high voltages, do not attempt. Only attempt at your own risk.
It should look like this. Note the battery in the bottom. Remove the battery. If you want to save the film, wind the film to zero frame and stop. Any further and the film will not be accessible. Just hold the shutter button down while turning the film advance wheel. Keep cranking on that thing! Pop the cover at the bottom to get the film out.
Carefully (or not) remove the plastic case by releasing the various tabs.
…and more tabs, 2 of these in the front.
Remove the cover and you should see the strobe circuitry.
Release the one tab locking the PCB in place and remove the unit carefully.
Here is the strobe unit.
Locate this component.
The metal contact (red arrow) here will be at about 200V when the circuit is charged up, so avoid touching this tab. Unsolder the component (yellow arrows) and remove it.
In its place, install the SIDAC. It’s bidirectional, so it doesn’t matter which way you insert it. Solder it in place. Here is the datasheet for the SIDAC.
The hatched area are the charge switch contacts. You need to connect a suitable on/off switch here.
Here is the completed unit with battery taped in place and the switch installed.
Remember: 200V! And the trigger voltage gets boosted to around 2000 to 4000V or so, so don’t go pokin’ around!