It is possible to add a hyperlink in text and link to an external website using the following steps; 
1. Open the text asset, highlight the required text & select the Insert gomo actions icon

2. Select Add action and choose the External web link option. You can then set the URL in the Result field. Click Update actions to confirm the change
3. Select Apply

4. Save the change in the Editor

5. Once saved, the text asset will appear underlined in preview