```javascript
const sdk = require('node-appwrite');

const client = new sdk.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

const functions = new sdk.Functions(client);

const result = await functions.updateVariable({
    functionId: '<FUNCTION_ID>',
    variableId: '<VARIABLE_ID>',
    key: '<KEY>',
    value: '<VALUE>', // optional
    secret: false // optional
});
```