Hi Sonali,
Permissions in WordPress and in this plugin are explicitly tied to specific capabilities and not roles. Typically the point of creating custom roles is so that you can assign a very specific combination of capabilities to user and also signify that they are a member of that user role group.
The Advanced section of the Dashboard Access settings does support custom capabilities, so if you were to create a custom capability that only users with your custom role would have, then you could set that role as a requirement for access. Note that you would want to make sure that your account and your other administrator accounts were also assigned that custom capability so that you don’t inadvertently lock yourself out of your site.
Hope that helps.