Hi Jlozolla,
What you've posted and what you're asking to do don't match. Are you trying to add the Channel numbers from Sheet1 into the drop-down list, or - as your current code attempts - are you trying to load the sheet names into the drop-down list?
To load the sheet names, change:
to
Your code for CommandButton1 should then work to put whatever you enter into the Serial box onto that specific sheet in the next available row (and into column B).
If you're trying to load the Channel numbers into your drop-down list, change:
to
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