```kotlin
import io.appwrite.Client
import io.appwrite.coroutines.CoroutineCallback
import io.appwrite.services.Databases
import io.appwrite.enums.RelationMutate

val client = Client()
    .setEndpoint("https://<REGION>.cloud.appwrite.io/v1") // Your API Endpoint
    .setProject("<YOUR_PROJECT_ID>") // Your project ID
    .setKey("<YOUR_API_KEY>") // Your secret API key

val databases = Databases(client)

val response = databases.updateRelationshipAttribute(
    databaseId = "<DATABASE_ID>",
    collectionId = "<COLLECTION_ID>",
    key = "",
    onDelete = RelationMutate.CASCADE, // optional
    newKey = "" // optional
)
```