New campaigns can be automatically added to a certain Performance Group and then the optimization starts - see how in this article.
To undo this action just do the reverse:
click on the three dots under "Action"
Choose "Set Default for an account" from the drop down
by clicking on the Account on the right side un-do your selection or exchange your selection by choosing a new account from the left side by clicking on it.
Confirm your settings by the blue button "confirm"