It is generally best practice to notify your insurer as soon as possible, this is usually stipulated in the policy itself. In some cases, the policy will not cover the legal costs if more than 30 days have passed since you became aware of the potential claim. Your insurer may refuse to cover the claim at all if you notify them of the dispute after the applicable notification period.
When notifying your insurance provider, you will most likely need to complete a form, providing a summary of your claim. After fully assessing the claim and the likelihood of it succeeding, the insurer will then advise you if your claim has been successful or not.