Oven thermometers are cheap, but barring that, use inexpensive canola or vegetable oil sparingly; just enough to make it shiny, and turn the knob to 350F (or whatever setting you use by default when baking or cooking).

If the coating turns white, recoat with oil and try a lower temperature or less time. Cast iron is an extremely old technology, and was common back in the days of wood stoves. It doesn’t require precision instruments to maintain it.

If you somehow ruin the seasoning, you can always scrape it with steel wool and try again. I once forgot a mini skillet in a frequentLy used propane grill for ~ 3 years, then left it outdoors with a burnt off coating for winter or two. I spent 5 minutes scrubbing rust off it in the sink, then oiled and seasoned it. We use it for sunny side up eggs these days.

Thanks! I'll give it a try.

In my country everyone has an electric oven, so you can set an exact temperature.