// Create mobile platform. The ID can be found in the documentation.
// https://developers.google.com/adwords/api/docs/appendix/platforms
Platform mobile = new Platform();
mobile.setId(30001L);
AdGroupBidModifier adGroupBidModifier = new AdGroupBidModifier();
adGroupBidModifier.setAdGroupId(adGroupId);
adGroupBidModifier.setBidModifier(BID_MODIFIER);
adGroupBidModifier.setCriterion(mobile);
// Create ADD operation.
AdGroupBidModifierOperation operation = new AdGroupBidModifierOperation();
operation.setOperand(adGroupBidModifier);
// Use 'ADD' to add a new modifier and 'SET' to update an existing one. A