How can i reset the new Photos App on my mac? I chose the wrong photo library when starting off the app, but i want to start over with another library. What can i do? PLEASE ANSWER ASAP!

Close Photos.

Find the Photos library that you have just created. It's probably in your User>Pictures folder. Drag it to the Trash, and empty the Trash.

Open Photos while holding down the option key. It should then give a list of the different iPhoto libraries you can import. house the one you want, and you're away.

Launch Photos again, but hold down the alt/options key ⌥ while double clicking the Photos icon to launch the app. This will bring up the library chooser panel. select the library that you want to migrate to Photos.

After Photos completed the conversion, open the Preferences and select the new library as the main system library on the General tab of the Preferences.

Then you can delete the other migrated Photos library.