You can use the Lcase request to change all characters in a string field to lower case.
Note: The information in this article applies only to retired products, ArcView GIS versions 3.x.The instructions described apply to the Avenue programming language, which is specific to the ArcView GIS application. For ArcMap and ArcGIS Pro, this procedure can be done using a Visual Basic or Python expression. In ArcMap or Pro, open the Field Calculator, and click 'About calculating fields' for examples of field calculations.
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