2004 Mitsubishi Endeavor Install Spark Plug

The manuals don't show any procedure for this. This is usually the case when it is a straight forward operation that doesn't require removal of other components.

See the guide below on changing spark plugs, not vehicle specific, but it will show you what is involved


https://www.2carpros.com/articles/how-to-change-spark-plugs

I changed the spark plugs and noticed oil on them. Is that normal

Most likely slight leak from valve covers. if not excessive , smoking or pooling in plug hole you can live with it repair at latter date.

I was doing the spark plug change when i find that the spark tube and the spark plug had oil, i checked the first 3 on them and the 3 had oil, i worried about it because i know its not normal....can i still use mi endeavor?? And what do i need to repair it?

You would need to replace the spark plug seals. If the oil is minimal, it would not cause any problem but if too much oil is in the plug tubes, misfiring can occur.

I believe this car has denso iridium plugs When is the recommended tune up and would bosch fusion iridium give me better gas mileage and last longer? Manual claims tune up at 60k while denso plugs claim over 100k. No performance issues just ok gas mileage at about 20mpg on highway driving. Would like to get more. Claim is 22mpg on highway.

Denso is one of the brands that OEMs use quite often and are quite good. European OEMs use Denso and Bosch. 6 of one, half a dozen of the other. You could upgrade coil(s). You could change the air filter for a high flow one. Plug gap is spec'd at .029-.031 inch. You can increase it to .032-.033, which will create a hotter spark, but also put more load on the coils.