2gext vs 5 gext on a Dell

I have set up AC750 WiFi Range Extender and I can connect all of my devices to the 2gext connection.  However, that connection is a little slow.  So I want to connect to the 5gext connection.  I have successfully connected 2 phones, an HP laptop (Windows 7) and a Kindle to 5gext.  I cannot connect my two Dell computers (Windows 10) because I don't even see the 5gext connection in my connection list.  Is it a Dell issue?  Or a Windows 10 issue?  Any ideas how to fix this issue?