Call United Airlines and tell them you cannot make the trip. they will cancel the ticket and, for most tickets, you can apply a portion of the ticket value to another international ticket issued and flown within 12 months. Note that there are exceptions for some consolidated or discounted tickets in which the full value is forfeited.

Then make a claim with the insurance. if the policy covers cancellations (either for a covered reason or if the policy is a "cancellation for any reason policy") then they will typically cover 75% of the cost.