Good, so you can select data from the database.

Before the row you can select, you can place radio buttons with as value
a representation of the primary key of the record (the customer number
for example).

Then, when the page is submitted, you know the record to edit.

Selecting the data to edit is something you already can: it's similar to
what you already have.

Editing the information is almost trivial, once you know two things:
1. What record to update
2. How to update a record

For point 1, add a hidden form field that contains a representation of the
primary key of the record being edited.

For point 2, read up on update statements and how to set SQL parameters.
That is, read the relevant part of any SQL manual, and the API for
java.sql.Statement and java.sql.PreparedStatement.