How to send a message to a specific subscriber among the subscribers?

Hi everyone.
How to send a message to a specific subscriber among the subscribers?

```
func (r *subscriptionResolver) Message(ctx context.Context) (<-chan string, error) {

randomString := make(chan string, 1)
go func() {
<-ctx.Done()
}()

randomString <- randString(8)

return randomString, nil
}
```