To apply a custom data role to a field, you need to select the data type of the field and then choose the data role from the list of available roles. This will validate the values in the field against the data role and mark any invalid values with a red exclamation mark. To fix the invalid values, you can use the Group Values option and select the Spelling algorithm, which will group values that are close in spelling and replace them with the most frequent value in the group. This will help you standardize the values in the Material field and match them with the Role1 data role. References: The information is based on the following sources:

Use Data Roles to Validate your Data - Tableau

New in Tableau Prep: Automatically identify data quality issues with Data Roles