Really pretty easy to take apart. May prove hard to type out but I'll try.
1. field strip.
2. remove guide rod,spring,barrel.
3. take a flat screw driver and remove the extractor from the slide. To do so put the blade of the screw driver under the lip like a case would sit and pry the opposite direction of the spring tention and also forward at the same time. Should just pop loose easy.
4. right safe lever just drops out. You may had to push the firing pin in a little to release the lever.
5. rotate the safe lever on the left side counter clockwise past where safe would be until it slides out. There is a little peg that has to line up with the groove. Sort of like when popping the slide stop out to remove the slide. I mean the peg / groove is simular. Again you will have to push the firing pin in a little to allow the lever to come out the side of the slide.
6. the firing pin will pop out (maybe across the room as it is under spring pressure)
Assembly is reverse except I use a wood dowel to push the extractor back in place. Long dowel thru the slide where the barrel would normally sit.
There is a write up about taking a P89 totally apart by Berettapistols. This would show pictures etc.
Hope this helps,
I would spray REM oil in the safety too.