You can't do that at the moment.
The change is still being worked on, so I won't go into too much detail here, but the idea is that newcomers to the site will no longer be able to
- edit answers that have been written by other contributors
#->#newcomers can edit their own answers
- post answers to questions that have already been answered
#->#newcomers can post answers to unanswered questions
This change was implemented because a lot of newcomers tend to use the ability to edit answers posted by other contributors and the ability to add multiple answers to a question to post unwanted [spam, abuse, hawk] and low-quality content [unexplained answers, copied content].
So in an effort to protect the content that is already on the site, the activity of newcomers is limited as described above.
I will come back with more details about the change in a couple of days' time, so stay tuned for more info on this! :D