Go to Admin Settings from the Home Page.
Navigate to Activities and select the Activity Form where you want to enable field history.
Click +New Addon and choose Field History from the list.
Open Field History from the addons list.
Click Search Fields and select the activity form fields for which history will be stored.
Choose History Limit Upto to define the duration for which history will be retained (Today, Yesterday, or a specific number of months).
Select User Selection and choose the required History Fields.
Click Save, then save the activity form to apply changes.