is there a bus from hendaye train station to biarritz station
The train is the most obvios way of getting between two stations.
There is a bus but as suggested above why not use the train, it will be quicker. Use en.voyages-sncf.com/en to find train times.
However if you must have a bus then they are provided by http://www.transports-atcrb.com
Bear in mind that the train station in Biarritz is not in the centre, it is about 2km out of town. To get from the station (called Gare La Négresse) to the city centre you need to catch a bus with http://www.chronoplus.eu