This has been done to death.
Ok you need a rectangular plate to fit on the side of the EGR valve and an oval plate at the bottom of the EGR valve.
If you fully blank the EML light will show up and annoy like buggery unless you get a remap.
However if you get the SEMI blanking plates (holes in them) then no EML will show up.
You can put the metal gaskets back if you want but it doesn't make a difference. Benefits are lower down power, preserve the life of the EGR valve and not cleaning it all the time.
Be sure that the engine is cold, if you do it whilst the metal is hot and soft you risk pulling the threads out.
Do not over tighten, just enough or again you will pull the threads out.
One blanking plate will be pointless, you really need to do the both.