How do you change the default email server in CometBird from Hotmail to Verizon?
Cometbird is a web browser. It has no email server, default or otherwise.
Hotmail is reached through a web site, at a particular url.
Verizon Webmail is also reached through a web site, at a different url.
Now presumably you have bookmarked the Hotmail site. You can simply visit the Verizon mail site manually, and when there, set a new bookmark for it.
You may have a desktop shortcut that fires up your browser and goes directly to the Hotmail web site.
If you want to create a similar shortcut for Verizon then you should study the existing Hotmail shortcut and notice where and how it would have to be changed to point to Verizon instead.