Collapsible/Popup section for Classic UI at SC item data screen

We have 10 custom fields that are displayed for user input in Classic UI for SC item data screen using metadata. The custom fields are visible and editable and working perfect.
Now, we have a requirement to put all the 10 custom fields under a collapsible/popup section, such that when user expands collapsible section or clicks on link to display popup, the custom fields are visible and editable and whatever values are entered by user in the collapsible/popup section for the custom fields are saved in system.
Kindly provide the detailed steps for achieving the above requirement urgently.