Regardless of any industry related training that you have been through, you will need to complete training specific to Regional Express.
If you do not have any industry-specific training, perhaps you have training that would be transferable to this role (IE: Sales, Safety, Customer Service, Technical, etc). Walk the interviewer through any on-the-job training you feel would be helpful.
"I have taken industry-related safety and customer service training with company ABC. In addition to this training, I have four years of industry experience."
"Although I have not taken specific airline related training, I do have some current certifications that I believe will be helpful. These include CPR, First Aid, and WHMIS training."