Unable to get and set values to a custom field via Zendesk App

Following is my code snippet. 

const getAccountNameFunc = async () => {

const myData = client.get('ticket.customField:custom_field_4590824941204')
client.set('ticket.customField:custom_field_4731199018772', myData['ticket.customField:custom_field_4590824941204'])

}

Am I doing something wrong ? I think the client.get returns an object. But I am not able to use the data received to set the value of another field.