Make sure CRISP is part of your hardware configuration, if it isn't already there then add it with Micro-Manager Window > Tools > Hardware Configuration Wizard…. See https://micro-manager.org/wiki/Micro-Manager_Configuration_Guide if you need further guidance on how to set up your hardware configuration.
The Plugin comes default in current versions Micro-Manager; if you don't have it in Plugins > Beta, update Micro-Manager to the latest nightly build.
If you would like CRISP to maintain focus at a certain position, but the error isn’t 0, use the Reset Offsets button to make your desired focal position have “0” error.
Further Reading Refer to CRISP : Continuous Autofocus System for a description of CRISP operation and troubleshooting guides.