Hi Sindhu,
Follow below steps:
1. Create a parameter with all selected and string as the data type of parameter.
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2. Now add a calculated field to search the product with those letters and display them.
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3. Add the created field onto row shelf and show parameter on sheet.
4. The sheet would be like below before typing any string/characters.
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5. Now type any characters, those products that match product would show up.
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Hope this helps you.