The easiest way how to convert drawings saved in the OpenDocument format (.odg) is to use one of the open source office suites like OpenOffice or LibreOffice, because their graphics apps works with ODG format by default. Export to Visio might be a little problematic, but the latest version of the Draw apps supposedly support VSDX format, which should allow odg to vsdx conversion.
Open ODG file Open VSDX file