Reset checkboxes to false

How about this modification? I think that there are several solutions for your situation. So please think of this as one of them.

Modification points :

• The reason of the issue is values[i].setValue(false);. values[i] is an array. Please use the range for setValue().
  • But to use setValue() in the for loop leads to higher cost. So in this modification, I used setValues().
• Put "false" to values, if values[i][j] is "true".
• Put the modified values to the sheet using setValues().

Modified script :

var dataRange = sheet.getRange('A3:A');
var values = dataRange.getValues();
for (var i = 0; i < values.length; i++) {
  for (var j = 0; j < values[i].length; j++) {
    if (values[i][j] == true) {
      values[i][j] = false; // Modified
    }
  }
}
dataRange.setValues(values); // Added

Reference :

• setValue()
• setValues()

If this was not what you want, please tell me. I would like to modify it.

Update:

You can now use range.uncheck() directly on the range

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Alternatively, Since you want to uncheck everything in the range (and all of the range have checkboxes in them), just do:

sheet.getRange('A3:A').setValue(false);

without checking/looping.