Mnemosyne Clinic for Memory Modification is a clinic for memory regeneration. The clinic's ad promises to restore memory to "natural range" using a spell. The Clinic's slogan is "Helping witches and wizards find their marbles since 1426". The Clinic also advertises in the Daily Prophet that they perform charms to help fix up faulty memories. No word on whether they help you forget things you'd rather not remember, or - alas - on their location, though Diagon Alley is probably a fairly safe assumption.