"Oven repair" is a global achievement; if you repair the oven in one save, you won't get the reward if you repair it in another save.
This seems unintentional, considering both "Clean toilet" and "Clean sink" are per-save advancements.
Viewing post in Voices of the Void 0.8.2 Bug Reports
You need a screwdriver and a wrench, which you can find on the workbench in the garage.
- Hold your screwdriver and interact with the oven.
- Click on all the screws to unscrew them and remove the cover.
- Back out and put the screwdriver away; you need to do the next step empty-handed.
- Interact with the oven again and rewire it.
- Click on a red output pin to select it.
- Click on a blue input pin to connect it to the currently selected output pin.
- If you hear a sparking sound, try again - that's not the correct output pin.
- Do this for every pair of pins.
- Once all the pins are connected, back out again.
- Hold your wrench and interact with the oven again.
- Click on every input pin.