How do I reset object numbering in magic sheets?

I'm making a magic sheet with arrays of lights. I delete some, I want it to reset the numbering from the point where I deleted.For example, I want to make an array of 6 par cans and number them channel 1-6. Then I copy them and paste and it automatically makes the next 6 7-12. Good. Then if I delete those six, the next number starts at 13. I want it to start at 7 because that is the first unused number.

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