You can create Primary claims that include the Secondary insurance's information automatically. In order for you to do this, you need to make sure you have already saved both a Primary and a Secondary insurance company in your client's Billing and Insurance Settings page. Then, scroll to the bottom of that page and click on the "Enable Additional Fields" option. This will reveal multiple options for you to edit your claims. The very last option in this list is the "Include secondary insurance info on primary claim?", make sure you set this to Yes and hit Save.
Keep in mind that the "Include secondary insurance info on primary claim?" option will only be present if you have already saved the Primary and Secondary insurance information in the client's profile.
From then on, every primary claim you create will include the secondary insurance information in box 9 of your Primary claim.