Which product(s) are you asking about?
If you downloaded and installed sound libraries 140 or so days ago you may not have used IK Product Manager since it was not available at that time but if you did use it the IK Product Manager FAQ at
https://www.ikmultimedia.com/faq/index.php?id=1384 and the manual should be very helpful in locating downloaded files as well as specifying the default location of your sound library installations.
If you've already installed the libraries, some users prefer to back up the whole drive with the libraries already installed (you can use programs to clone a drive, or copy to another external driver or cloud backup provider, etc) so they can just copy and link to that if and when they need to. Or you can take your downloaded sound library installers and back those up with a program and/or cloud service.
Note that the installers for the applications themselves do not need to backed up as only sound libraries have the 180 day expiration.