Wise Pilgrim is great because it has a feature to contact the albergues via WhatsApp and composes a message for you in Spanish (or Portuguese or French depending on location).
Here's a post I made earlier this year about how to use the feature:
You will be walking during one of THE busiest periods for pilgrims starting from St Jean Pied de Port, so I would recommend that you book your accommodation up to or through Pamplona before leaving home. After that you will have a better idea of the distances that you can cover each day, and there are more intermediate towns to stop in and the pilgrim traffic tends to spread out more.