Once you have Registered the iRig hardware then AT4 should be listed in the IKPM (IK Product Manager).
If not then please contact
Sales/Account Support, via here. You will be able to search the FAQs first, but if they do not resolve your issue, there is a link at the top of the Search FAQs page to a Support form. Sales Support can look at your Account and see what's going on.
Response time normally is within 2 working days (US (East Coast) Business hours, generally), but in the current circumstances please allow some more time. Administrators and Moderators here cannot access your Account.
Or, have a look in your User Account / My Products area. Find AT4 and click on Past Releases - you should see the AT4 download, for v4.10.0 there.