If the tooth enamel is fully destroyed then nothing can repair the fully damaged tooth enamel.
However if the tooth enamel is just starting to wear off or is just starting to become damaged then yes using some Remineralizing toothpaste can really work to help restore the damaged or lost tooth enamel.
You must start using the Remineralizing toothpaste as soon as you start getting damage to your tooth enamel for it to properly work.
However cavities cannot be repaired using Remineralizing toothpaste but it can help prevent future cavities from appearing and help demineralized areas be repaired.
The Remineralizing toothpaste helps to replace the lost minerals in your teeth and tooth enamel so it does help somewhat but only if you start using it before the teeth get too bad.
If you have a deep cavity or lost enamel that has gotten too bad then only a dentist can help with the deep cavity by filling it in but sometimes they cannot help with bad eroded tooth enamel.