How do I separate an enchantment book with multiple enchantments?

I have been enchanting books in minecraft lately since I wanted looting for my pick axe and I finally enchanted a book and got looting. I then realised I had silk touch on it aswell, how do I separate them since the looting won’t work with silk touch?

Simple answer: You can't.

You need to choose between the silk touch and looting, by either having a looting sword, or a silk touch tool. Without discarding the book and cheating for a looting book and cheating for a silk touch book, there is no way to do that in vanilla survival Minecraft. If you want a looting sword and a silk touch tool, you need to get a whole new book, or manually enchant the sword and pickaxe. See Fastest way to get enchanted books?.