How do I assign value to a repeated oneof field in a protobuf message?

I have a protobuf message CoverageReport like this:

 message Deductible {
double amount = 1;
string currency = 2;
}
message Insurance{
string type = 1;
string policyNumber = 2;
string agreementName = 3;
string appliedTo = 4;
string validFrom = 5;
string validTo = 6;
Deductible deductible = 7;
}
message Warranty {
string type = 1;
string warrantyType = 2;
string agreementName = 3;
string appliedTo = 4;
string validFrom = 5;
string validTo = 6;
}
message Coverage {
oneof item {
Insurance insurance = 1;
Warranty warranty = 2;
}
}
message CoverageReport {
bool coverageAppliance = 1;
repeated Coverage coverages = 2;
}

In my program I'm trying to assign values to a message instance, but I'm not sure how to assign to the oneof field Coverage which should then be appended to Coverages, like this
I get a response from an api, which i unmarshal into the struct CoverageReport which has similar structure to the protobuf. Then i need to create a protobuf message using the values from the struct. But it doesn't seem to work to asssign to the one of field!

type CoverageReport struct {
CoverageAppliance string `json:"coverageAppliance"`
Coverages         []struct {
Type          string `json:"type"`
PolicyNumber  string `json:"policyNumber,omitempty"`
AgreementName string `json:"agreementName"`
AppliedTo     string `json:"appliedTo"`
ValidFrom     string `json:"validFrom"`
ValidTo       string `json:"validTo"`
Deductible    struct {
Amount   float64 `json:"amount"`
Currency string  `json:"currency"`
} `json:"deductible,omitempty"`
WarrantyType string `json:"warrantyType,omitempty"`
} `json:"coverages"`
}
var coveragereport *CoverageReport
err = json.Unmarshal(body, &coveragereport)
var cr *vcsproto.CoverageReport
if coveragereport.CoverageAppliance == "Yes" {
cr.CoverageAppliance = true
}
for _, item := range coveragereport.Coverages {
if item.Type == "Warranty"{
var warranty *vcsproto.Warranty 
warranty.Type = item.Type
warranty.WarrantyType = item.WarrantyType
warranty.AgreementName = item.AgreementName
warranty.AppliedTo = item.AppliedTo
warranty.ValidFrom = item.ValidFrom
warranty.ValidTo = item.ValidTo
var coverage *vcsproto.Coverage
coverage.Item.Warranty = warranty
cr.Coverages = append(cr.Coverages, coverage)
} else {
var insurance *vcsproto.Insurance
insurance.Type = item.Type
insurance.PolicyNumber = item.PolicyNumber
insurance.AgreementName = item.AgreementName
insurance.AppliedTo = item.AppliedTo
insurance.ValidFrom = item.ValidFrom
insurance.ValidTo = item.ValidTo. 
insurance.Deductible.Currency = item.Deductible.Currency 
insurance.Deductible.Amount = item.Deductible.Amount 
var coverage *vcsproto.Coverage
coverage.Item.Insurance = Insurance
cr.Coverages = append(cr.Coverages, coverage)
}
}

Take a look in the generated code here.

You do not assign directly to the Warranty nor Insurance subfields, but directly to the Item field. so coverage.Item = {insurance/warranty} should work.

Also note that in your code you're assigning coverage.Item.Insurance = Insurance - you probably meant the second Insurance to be the variable insurance instead.