A notification poped up asking me to freeze unused apps which I did. Now how do I unfreeze them?

[AC Question]

I use a tecno C9 that runs on Android Marshmallow. A notification recently appeared and asked me to freeze certain unused apps which I did.
Now how do I unfreeze them?

 

[nahoku]

Where did the notification come from? What app gave you that popup? What apps did you freeze?