Reset New and Edit buttons

You will also need to reset the New and Edit button -where overridden- to Use the Salesforce Classic override.

1. Navigate to Setup, then Object Manager.

2. Click the object name that has overridden New/Edit buttons.

3. From the left, click Buttons, Links and Actions.

4. Scroll to the Edit/New buttons that are overridden and, on the right, click the downward arrow, then Edit.

   

5. For any overridden properties, select No override/Use the Salesforce Classic override radio, so that properties look like below, then click Save.

   

6. Repeat steps 2-5 for any other remaining objects that have overridden New/Edit buttons.

You can then proceed by switching back to the Lightning mode and overriding the buttons from Classic override to the Lightning component.