How to write data to session and pull it out to woocoomerce?

Question

WordPress

Good day. In general, the task is to make the choice of the region and city in the modal window, write it all down in the WP session and, when placing an order in woocoomerce, pull the region and city out of the session. Please tell me how to implement all this, I only know how to make a modal window. Googled, found instructions on how to work with the session, but I didn’t figure out how to make a choice in woocoomerce