What level of spell slot do I need to use to reassert control over a pair of mummies I created?

Question

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?

Answer 1

You need a spell slot of the same level as it took to create them — you need a 9th-level spell slot to reassert control over mummies (PHB, p. 229):

At Higher Levels. When you cast this spell using a 7th-level spell slot, you can animate or reassert control over four ghouls. When you cast this spell using an 8th-level spell slot, you can animate or reassert control over five ghouls or two ghasts or wights. When you cast this spell using a 9th-level spell slot, you can animate or reassert control over six ghouls, three ghasts or wights, or two mummies.