PeopleSoft change assistant is a standalone application delivered with PeopleTools 8.4x onwards. PeopleSoft change assistant can be used for applying patches and fixes for maintenance updates.
PeopleSoft change assistant grabs all the required information from the Environment Management Hub and uploads it to the PeopleSoft customer connection site. With this environment information, PeopleSoft customer connection will determine what updates should be applied to your environment.
When you access customer connection, you can get a list of all unapplied updates for your given application environment including any prerequisites. So you can download all the change packages and apply the fixes and patches to your environment with very minimal effort.
Make sure you setup environment name by going to PeopleTools -> PeopleTools Options
Enter the Environment Long Name and Environment Short Name parameters.
PeopleSoft delivers templates for each update in change packages. Whenever you apply updates by using the Apply change package option, change assistant will automatically loads the template into Change Assistant. You can add additional tasks and steps into the template.
Check your PeopleBooks for more detailed information on this.
Note: You can only apply application relates fixes using PeopleSoft Change Assistant. You can not apply PeopleTools fixes / Patches with change assistant. You should use Upgrade Assistant for that purpose.