Here is an update query to update the email address in Dimcustomer table.
update [dbo].[DimCustomer]
set EmailAddress = REPLACE( EmailAddress,'adventure-works.com','gmail.com')
Replace command is used to replace a particular substring a column. The syntax is Replace(column Name, Old String, New String)
Cheers,
Venkatesan Prabu .J
Head, KaaShiv InfoTech