As legal parents, are you unmarried and not in a civil partnership? Then there is a difference between whether the child (including an unborn child) was recognised before or after 1 January 2023.
Was the child recognised before 1 January 2023? Then you can apply for joint parental authority together using a form. This can be done online or in writing. A lawyer is not required.
Was the child recognised after 1 January 2023? If so, you will automatically have joint parental authority over the child, unless any of the exceptions apply. You do not need to do anything.