Usually you could go to Manage and check the boxes next to multiple APs, click on the edit icon next to ADD and then follow the same instructions as before, but unfortunately right now some of our bulk editing settings aren't working properly, including setting a static channel.
Another alternative would be to create an AP template for your models by going to Configure> Network Policies> Open the Network Policy in use> Go to the Device Templates tab within the Network Policy> Create a new template or open the existing one> Apply the static Channel you'd like to use> Push out a configuration update to all of the APs so they'll use the new template settings.
