Your institution's technical team should be able to provide a full list of your IPs. Please ask them to include IPv6 addresses if applicable. This complete list will ensure that your patrons can access Credo from anywhere in the institution.
Small institutions may be able to find their public IP simply by Googling "Find My IP Address" from a library computer:
https://www.google.com/search?q=find+my+ip+address
If we have your full IP list but you're experiencing access issues, copy the URL of the Credo login page and contact support@credoreference.com with this information. It will start with https://iden5.infobase.com... and contains further information to help us troubleshoot.