Before you get on the plane, make sure you have the contact number for your travel insurer. This can be the 24-hour helpline, or it can be the insurance agent you bought the insurance from.
If you’ve purchased the insurance online, do note the contact details of the website as well (e.g. the helpline or email address).
Ensure that a family member or friend knows the insurer’s contact details. On the off chance that you’re unable to contact the insurer yourself (i.e. you don't have a data connection or are incapacitated), they can reach out on your behalf.