how can i make new item drops from existed vannilla mob or block

You have to create a loot table with the namespace Minecraft and the exact same name as the block or mob in question. Then set it to whatever you want (it will override the vanilla drops, not add to them, so you have to put existing drops in there as well or the block will stop dropping them)

another way to do the mob item drop make make a procedure that uses the Entity Dies Trigger, the an If Entity Exists block.