Add a button to an existing tab created before

[m_ibrahim5LUN8]

I've created a revit addin before and add it in a new tab with panel, now I want to add new button to this tab but I don't know how. 

[jeremy_tammik]

Well, you will often obtain an answer faster by searching for it yourself, e.g., for "revit api add button to tab":

• https://duckduckgo.com/?q=revit+api+add+button+to+tab

The Building Coder shared a solution especially for this specific question back in 2013; it may be a bit out of date, but the basic principles probably still apply:

• https://thebuildingcoder.typepad.com/blog/2013/02/adding-a-button-to-existing-ribbon-panel.html