In order to login to SlickPic using Facebook or Google when using the mobile app, or the Lightroom and Photomechanic plug-ins, you will need to follow these steps.
First, go to your Account and click on Change Password at the bottom of the side menu.
If you created your account with Facebook or Google, you will not see the Old Password field here. Just enter and confirm your new password.
You will now be able to use this password to login to the app.