2.4 gigahertz smart devices

I upgraded my aunt's router to a newer one she had in her closet. Now the DSL will not support the smart plugs which require 2.4 gigahertz. I believe I should be able to set the Internet at 2.4 gigahertz. when I go into device configuration I am unable to continue to set that up. Today I am having trouble even getting into that advanced configuration with my with my access code. Pulling my hair out. She needs her smart plugs