Using reflection SetString

I have a struct like this one:

type ProductionInfo struct {
    StructA []Entry
}

type Entry struct {
    Field1 string
    Field2 int
}

I would like to change the value of Field1 using reflection but the reflect object returned always CanSet() = false. What can I do? See playground example.

https://play.golang.org/p/eM_KHC3kQ5

Here is the code:

func SetField(source interface{}, fieldName string, fieldValue string) {
    v := reflect.ValueOf(source)
    tt := reflect.TypeOf(source)

    for k := 0; k < tt.NumField(); k++ {
        fieldValue := reflect.ValueOf(v.Field(k))

        fmt.Println(fieldValue.CanSet())
        if fieldValue.CanSet() {
            fieldValue.SetString(fieldValue.String())
        }
    }
}

func main() {
    source := ProductionInfo{}
    source.StructA = append(source.StructA, Entry{Field1: "A", Field2: 2})

    SetField(source, "Field1", "NEW_VALUE")
}