If you use the option to book a guest, you can later convert this guest traveler profile into a full user profile.
You make the booking as described in the article Guest user bookings.
Afterwards, go to the user management in the company account.
Use the "Show guests" filter and then click "Apply filter" to display all guest profiles in the company.
Select the guest traveler profile that you want to convert into a full user profile and click on "User".
You are now in the master data of this profile and can store the correct email address of the user and assign the correct role to this user. To do this, simply follow the steps in the Adding a new user article.
After you have entered all the data correctly, click on "Resend invitation e-mail" so that the user can log in with a specially selected password.