I do believe the OP is saying that TT will not install Illinois forms in they try to update the program.
You can go here and see if this helps your problem.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/electronic-filing/state-install-e-file-u...
If that does not work contact Support and they should be able to help you with downloading a stand alone Illinois program (file) for you to install. Note I had this happen last year and that is what I had to do.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/turb[product key remo...
or
https://ttlc.intuit.com/turbotax-support/en-us/help-article/account-management/contact-turbotax/L2y9...
