I believe you have to apply at the town hall (Ayutamiento) which is in Santiago del Teide. However, you should first try their local office in Playa Arena. This is upstairs about half way along the shopping area, opposite the black sand beach, next to the Tourist Information office. They are very helpful, speak some English and will certainly be able to tell you where to apply. Alternatively, you could try the other council office just round the corner from Apartments Drago in Puerto Santiago, on thr same sude as.Dino's supermarket, a few yards further up the hill. They deal with car registration and other matters there. There is an annual charge which I think may be around 150 euros.