You need sandpaper from about 800 grit to 2000 grit. You also need a flat surface like a pane of glass. You also need a crap ton of elbow grease. If you lap the heatsink you also need to lap the heatspreader or it is a total waste of time. TBH lapping even done right is a waste of time imho.If you have lapped heatsink on your i9-10920X / i9-10900X how much of temperature drop you got, please?
Also, which tool you would recommend for heatsink lapping to someone that is completely inexperienced and clumsy like me?