Go to the line item's Settings tab.
Under "Adjust delivery", select one of the following Rotate creatives options:
- Evenly: Each creative is displayed equally at random.
- Optimized: Creative with the highest CTR displays more often.
- Weighted: Creatives displayed at a frequency you define.
- Sequential: Creatives display to each user in the order you specify.
Go to 'creatives' tab
For creatives SOV, Change the weight on 'weight' column
Read more at Google docs here