Assuming the dataset/model isn't shared to you (i.e. you are the author).
1. Download Power BI publisher for Excel and install https://www.microsoft.com/en-us/download/details.aspx?id=50729
2. Make sure you have published your Power BI report & data model to Power BI Service
3. Login to your MS account associated with PowerBI (in Profile section of Power BI ribbon created by step 1).
4. Connect to data in your workspace.
5. Depending on the data source, you must have data gateway set up (personal or on-premises)
Note: If model is shared with you by group member. You'll need Pro or Premium subscription.