SQL Database dynamic data masking with the Azure portal
In the Dynamic Data Masking pane in the portal, you see the recommended columns for your database. Select Add Mask for one or more columns, then select the appropriate masking function and select Save, to apply mask for these fields.
In details:
Enable dynamic data masking
Step 1: Launch the Azure portal at https://portal.azure.com.
Step 2: Go to your database resource in the Azure portal. [Select db1]
Step 3: Select the Dynamic Data Masking pane under the Security section.

Step 4: In the Dynamic Data Masking configuration page, you may see some database columns that the recommendations engine has flagged for masking. In order to accept the recommendations, just click Add Mask for one or more columns and a mask is created based on the default type for this column. You can change the masking function by clicking on the masking rule and editing the masking field format to a different format of your choice. Be sure to click Save to save your settings.
4.1 If possible locate the column with email addresses in the SalesLT.Customer table [If not seen skip to step 5]
4.2 Click Add Mask
Step 5: To add a mask for any column in your database, at the top of the Dynamic Data Masking configuration page, click Add Mask to open the Add Masking Rule configuration page.
[Skip steps 5-6 step if step 4 was successful]

Step 6: Select the Schema, Table and Column to define the designated field for masking.
Select the following
Table: SalesLT.Customer table
Column: [Choose the column with the email addresses]
Step 7: Select how to mask from the list of sensitive data masking categories.
Select Email ([email protected])

Step 8: Click Add in the data masking rule page to update the set of masking rules in the dynamic data masking policy.
Step 9: Type the SQL authenticated users or authenticated identities from Microsoft Entra ID (formerly Azure Active Directory) that should be excluded from masking, and have access to the unmasked sensitive data. [Skip] Step 10: Click Save in the data masking configuration page to save the new or updated masking policy.
Reference:
https://learn.microsoft.com/en-us/azure/azure-sql/database/dynamic-data-masking-configure- portal