I need to create a custom role group and members of this role group should be able to:

[Kailashj]

• Access O365 Admin Center and can create and update contact information of the users
• Add-remove members in DL
• Should be able to pull up reports and can run message trace report
• Change the current manager of a user object.

[#2]

There is currently no support for custom roles for the Microsoft 365 Admin center. If you need the users to be able to access it, you will have to grant one of the default roles, such as User administrator. If you only need access to the Exchange Admin Center, then a custom role should do. Follow the steps here: https://docs.microsoft.com/en-us/exchange/permissions-exo/role-groups