You should speak to your vet about identifying the underlying cause of the dandruff, rather than trying random "home remedies" which will do nothing about the true cause and may or may not be safe for your cat. While a cat can safely consume olive oil in extreme moderation for relief of constipation and hairballs, I have found no references anywhere to using it to treat dandruff.
According to PetMD, dandruff and dandruff-like symptoms can arise from nutritional deficiencies, allergies, infections, parasites, immune diseases, diabetes, and skin tumors; they recommend consulting with the vet to identify the underlying problem. None of these issues will be addressed by feeding olive oil in any quantity.
On another page on the topic, PetMD's top suggestion for relieving dandruff is, again, consulting your vet. Their full list of high-level suggestions is:
- Get Your Veterinarian’s Opinion
- Look Into Changing Their Diet
- Bathe Your Pet Regularly
- Try a Dandruff Shampoo [Designed for Pets]
- Get the Right Brush, and Remember to Use It
Once again, olive oil is not mentioned anywhere; under the diet header, fish and coconut oils are mentioned, but with the advice to consult the vet before adding them to an already nutritionally appropriate food.
Other sites have also recommended stepping back from over-bathing and hydration as further ways to alleviate the issue; both are good ideas in general, as cats rarely benefit from bathing unless it is truly necessary (and, as in humans, overgrooming can worsen dandruff symptoms), and are frequently dehydrated.
I am unsure where you came up with the idea of feeding olive oil to relieve dandruff, as I was not able to find a single source recommending it, either on reputable or questionable pet care sites. It is vital to remember that our pets have different digestive systems than our own, and many things that are perfectly safe for humans to consume may be dangerous or deadly to our pets; never feed any human food without first verifying that it is safe.