Navigate to your project by hovering over the "Projects" tab in the top left corner of IMS, and selecting "Project List." From here you can select the project you would like to edit, or use global search to find it as well. After selecting the project, navigate into the correct entity and class that you are looking for.
Click on the three dot menu at the top right and select "Class Preferences." From here, you will be able to scroll down towards the bottom, and select "Allow Over-Subscription for this Equity Class."
Click "Save" at the bottom right, and you are all set!