Inside a little cup, add the Hydrogen peroxide. (for one cover, you can add a spoon)

add around 1/10 of ammia (for a hydrogen spoon, you can add 10 drop of ammonia.

add a spoon of water. Mix the solution with a cotton swab.

You can now add gently some of the liquid with the cotton swab on the marks.

I recommand to add it to around ten marks. Then wait 30 minutes like this. You can then take a humid tissue to wipe it. The action of the solution will continue after that during some hours. For now, you can continue to add the liquid on other marks. Waiting for 30 minutes, wipe it, etc... For very hard removing mark, you can try to add the solution again after 1 hour, on the same mark.

Doing that during the day, near a well lighted window, give more results than doing it evening. Because the action of Hydrogen is connecting to the light.

Also, never shut or store your LD/LD, with the solution not perfectly dry.

Don't do that on thin paper. The makrs will disapear, but the paper will be damage.