If you did not set a password on the page where you created the wallet, you will not be able to set a password on it anymore. We recommend that you download the desktop version of Jaxx if you would like access to these features.
To access the feature in desktop, please go to top right corner of the wallet there are 3 horizontal white lines, click on them and it will bring up a list of options. Click “Tools", then click “Display Private Keys”. To encrypt it, in the same set of options, there is “ display backup phrase” where he can see and store his 12 word list