How can I set prices for Otto?

Pine provides a feature that activates price sync for all your products

By activating this option prices for all your products will be synced continuously to your Shop prices. It doesn't matter if the products were listed via Pine before. 

Therefore, click Channels -> Otto -> Settings 

Then tick the box as indicated to activate the price sync. If the box is not checked, the prices are transferred once when the products are listed and can then be edited manually.