I advise to attempt to repair a camera objective only if you have at least some technical experience (like knowing how screws behave and being able to determine the order of operations upon inspection, etc.) and have proper tool for the job! Otherwise I recommend to look for a professional!
1. Remove front cover.
2. Remove back cover by removing the screws that form an equilateral triangle. Don’t touch the other screws because they hold the parts of the aperture mechanism.
3. Unscrew the back lens group.
4. Unscrew the front lens group.
5. Turn the focusing ring to its close end.
6. Remove giude pieces in the back of the assembly that keep the inner helicoid from turning.
7. Remove the inner helicoid by turning it, mark where it separates.
8. Turn the focusing ring to infinity, there is a small screw in the back that stops the focusing ring from turning all the way around, remove that.
9. Turn the focusing ring counter clockwise, count the turns and note where it separates.
10. Clean the helicoids, the fine threads and the guide pieces thoroughly. You can use alcohol, benzyne or in the case of the outter helicoid you can wash it with dishwasher and a toothbrush under tapwater and then wipe it dry.
11. Lubricate the fine thread on the focusing ring and screw it back into the stationary part while counting the turns. Put back the stop screw to keep the focusing ring in place.
12. Lubricate the helicoids and the guide pieces and reassemble everything.
13. Screw back the rear lens group. Reassemble the back cover.
14. Screw back the front lens group and the front cover.