Hi @Afhaz Ahmed and welcome to the community,
If you don't have access to admin.atlassian.com, then you are not and org admin and you can't reactivate a user. In addition, "Managed Accounts" will be present only if you have verified your domain and claimed the accounts of the verified domain. Are the two previous statement valid for your case?
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.