which spell i need to use and the correct form to use it? i tried some by the name and description, but i couldn't.

Hi, you need the Essence Extraction spell. It takes up a lot of mana, and you must be holding a (regular) Astral Diamond in your offhand while you continuously channel the spell at an Imbuement Altar to charge the diamond. It destroys the altar.

but i need the charged astral diamond to make the imbuement altar

Yes, the above process results in a charged astral diamond