Step 1- The Patron Registration Form

To get to the add patron form go to Patrons > New patron and choose any patron category from the dropdown list. 

As it is possible to add or remove items from the Patron Registration form the content may vary from site to site, however, it should look something like this:

Take note of any fields that you would like to remove.

Step 2- Removing Field(s)

Go to KOHA administration > Global System Preferences and search for BorrowerUnwantedField. 

This will bring you to a page of system preferences. To remove a field from the form the name of the field, as it appears in the borrower table on the KOHA database, needs to be put into the system preference BorrowerUnwantedField.  

For example, if a library wants to remove the Date of Birth Field, they would input dateofbirth in the box in the BorrowerUnwantedField system preference.

When removing multiple fields from the patron registration form, each field inserted into the BorrowerUnwantedField system preference needs to be separated by a vertical bar.

The patron registration form is divided into blocks of fields (Patron Identity / Guarantor Information etc) If you remove all fields relating to a particular block, the block will no longer display.

After this edit, the Date of Birth field no longer appears in the patron registration form.

To find the details of the fields on the borrower table view the database schema and look up the version of Koha your system is on and find the borrower table in the schema list.