To auto number the current entity and all related child entities to follow a hierarchal order in which the root entity's number is prefixed to all children's numbers recursively and assigns siblings numbers starting from 1 all the way to the total, focus your attention on the toolbar. Find the dropdown labeled More and click on it to expand it.
With the More dropdown open, select the option labeled Auto Number and the Auto Number popup will appear.
From there, you can specify if you want only the first level of children, or its immediate children to be auto number, or leaving it off to apply to the children of its children. You can additionally specify the number of the parent you wish to use for the root entity, which would then be prefixed to all its children entities. When you have selected the settings you desire, click Run and await the auto numbering process to complete. Otherwise, you can cancel any changes.