There are a few different ways to reassign deal ownership. Please keep in mind that you may have limitations on the list of users that appear in the dropdown depending on your user role. Refer to an admin on your account with questions regarding your user role permissions.
Reassign from the Deal Profile Page
To reassign a deal to another user from the deal profile page, click on the current owner's name and choose a user from the dropdown menu. The new owner will receive an email notification that a new Deal has been assigned to them in Pipeline.
Reassigning deals from the Deals list view
Reassign individual Deals in list view by clicking on the owner cell in the list view and selecting a new owner from the dropdown list of users.
Reassign deals in bulk by selecting them using the checkboxes on the left > More > Reassign then select the user from the list.