When signing up as an organisation, you'll have the option to claim your Do-it.org organisation and create a new Do IT account.
On the signup or signin screen choose the option to Login with Do-it.org.
Here, submit your current Do-it.org email.
You will receive confirmation the email is recognised.
And be sent an email containing a link to access your new account.
Click the Set my new password link in the email and you'll be taken to a screen to set anew password for your Do IT account (you'll be signing in from now with the email address of your old Do-it.org account).
After setting your new password you will be taken to the Admin Dashboard for your organisation.
Please note that currently only live opportunities you had on Do-it.org will sync over.