After Olleros de Tera at one point you will come to a crossing where there are two arrows. One pointing to the road and one pointing straight on into the greenery. If you have the Via de la Plata Guide app then the camino route will show as the one that goes off into the greenery and on the road under the road arrow there will be "bicicleta" written.
Warning. Unless you are ready to walk on an overgrown barely 20-30cm wide forest path with spider webs in your face and some very steep and very muddy ascent and descent where the path takes you all the way down to the river that is currently occupying some parts of the route (aka flooded) and then makes you climb back up to the road (with some false routes going god knows where), I would suggest taking the road.
I attached the part (I just got back onto the road when I took this screenshot) and also the last ascent to the road.
Warning. Unless you are ready to walk on an overgrown barely 20-30cm wide forest path with spider webs in your face and some very steep and very muddy ascent and descent where the path takes you all the way down to the river that is currently occupying some parts of the route (aka flooded) and then makes you climb back up to the road (with some false routes going god knows where), I would suggest taking the road.
I attached the part (I just got back onto the road when I took this screenshot) and also the last ascent to the road.