In an existing database, we have discovered some text entries where characters with accents were badly encoded.
The following query:
PR.Product_Ref__ AS ProductCode,
CONCAT(P.Name, IF (PR.Misc <> '', CONCAT(' ', PR.Misc), '')) AS Name
Product AS P
Product_Ref AS PR ON P.Product__ = PR.Product__
Name like "%é%" AND
PR.Product_Ref__ IN ( 659491, 657274 )
You just can simple detect all the occurrences that you want to correct and the use a simple update clause to make the substitutions.
Example for the case that you describe:
UPDATE Product SET Name = REPLACE(Name, 'Ã©', 'é') WHERE Name like '%Ã©%'
You can run this updates directly in mysql databases, using the command line or in a specific mysql user interface client application. Or if you like, using php functions that run sql statements in the database.