I want to know how I can convert geoJSON data to GPX format.
A general answer: use ogr2ogr from command line
Or, try finding a library in your language of choice.
There is a free REST API for this
Simply POST GeoJson Data to an endpoint, and view the POI in Augmented Reality browsers(wikitude) , google earth, google maps or any GPX(track and route), KML, ARML supported app in real time.
Just create an AppKey, and check out the code samples in curl,java,node,php,python,objective-c,ruby, and .net.