Big thanks Erel, now there it's code that is working almost good for me
Try
Dim i As Intent
i.Initialize(i.ACTION_VIEW, "file://" & File.DirRootExternal&"/myFolder/" )
i.SetType( "resource/folder" )
StartActivity(i)
Catch
Msgbox("Missing default file explorer", "Error")
End Try
On older Samsung Galaxy S2 I have always error that there isn't any intent to do that, so I put try catch
BTW on this old samsung is explorer named "MyFiles" in "settings" .... but it didn't start
on newer android phones start some other applications which are registered (maybe) as file explorers