In Lightning Salesforce: Add to Layouts page in Classic and Lightning. From a record click the gear or setup icon in the upper right corner of the page > select 'Edit Object' > select 'Page Layouts' > select the layout you want to update > this should bring you to the same edit layout page you see in Classic. Click 'Mobile & Lightning Actions ...
1- Create a new visualforce page. - Press on the 'Setup' icon in the top menu. - In the left Search box type the text visualforce. - Press on the 'Visualforce Pages' link. - Click on the "new" button. - Give it a name. - Turn on the "Available for Lightning Experience, Lightning Communities, and the mobile app" checkbox.