In the DMG the Animate Dead and Create Undead spells state that
you must cast this spell on the creature before the current 24-hour period ends. This use of the spell reasserts your control over up to three creatures you have animated with this spell, rather than animating new ones. Or 4 if the spell is animate undead
However if I was to cast Create Undead which allows me to summon two mummies at a 9th level spell slot can I still use a level 6 spell slot to reassert control over them after the 24-hour period?