LTS pre-release testing tries to identify problems that users will experience as they upgrade from previous LTS versions to the new LTS version. It also tries to identify areas that need to be described in the LTS upgrade guide.
Look for issues that surprise you when interacting with Jenkins 2.289. Discuss those issues in the chat channels. If that discussion leads to "it is a bug", then submit an issue using the
"How to report an issue" instructions.
Review the changes between Jenkins 2.277.x and Jenkins 2.289. Identify any that you believe could be higher risk to users. Test that they are well-behaved in Jenkins 2.289. If they are not, report an issue.
Review changes made to Jenkins versions after 2.289 (see the weekly changelog) and consider if any of them should be flagged as a candidate to be backported to the LTS.
Thanks for your willingness to help with the LTS pre-release testing!
Mark Waite