Displaying data of an authorized user in the Bitrix ordering field?

Question

1C-Bitrix

It is necessary to develop a handler that will automatically pull data from the site database and insert it into the checkout field. The bottom line is that when a user registers on the site, he enters his data, logs in, and when it comes to placing an order, the user needs to enter his data again, name, phone number, mail, etc. How can I make it so that I don't have to re-enter this data? Don't throw stones, I'm still learning, if possible, describe in detail how to write a handler and where to push it in the end so that it all works.