You can find the contact details in the Revolut app. Go to the 'Hub' tab on the main navigation bar of your app, tap 'Insurance', select your insurance, and press 'Get help'.
Please be aware you will be requested to provide a copy of relevant documents such as for example the receipt of the item or the event ticket, police report in case of theft as part of the claim process.
Please see the Terms & Conditions in the app for more details.
You can access them in the app by going to Hub → Insurance → select the type and click on 'All documents'.