Changing familiars shapes while they are ”dead”

So, one of my players is a wizard with the find familiar spell and in the last session they had to deal with some hags. While they were scouting a manor one of the hags attacked his familiar and killed it. I am quite unsure about the wording of the spell, because to me it seems like when you recast this spell you get the same familiar as you had previously. I have a problem with this part of the wording: ”When the familiar drops to 0 Hit Points, it disappears, leaving behind no physical form. It reappears after you cast this spell again”. Can it’s form be changed when the spell is cast again? Or does he have to cast the spell once to get the familiar back and then cast it again to change its shape? Thank you for your answers in advance.