There are different command buttons on entity forms and views. We can use these command buttons to initiate different actions. All the new forms, which are also known as updated forms, contain command buttons, while all the old forms still contain ribbon buttons. In the following screenshot, we can see the command buttons of an entity form and a subgrid:

We can add new command buttons or modify the existing command buttons by modifying RibbonDiffXml:

We can customize RibbonDiffXML manually by exporting our solution, which should include our entity, to where we want to add a new custom command button. However, adding a command button manually can be error-prone, so it is recommended to use a tool to add command buttons quickly. One of the popular tools in the Dynamics 365 CE community is Ribbon Workbench. This tool refers to our solution and modifies the ribbon definition by simply using drag and drop controls on the command button editor. Make sure that you keep your solution components to a minimum; otherwise, customizing and publishing changes can be time-consuming.