That isn't Tolle's. It's been said many ways before, like the Serenity Prayer written by the American theologian Reinhold Niebuhr (1892–1971) [1]:

God, grant me the serenity to accept the things I cannot change,

courage to change the things I can,

and wisdom to know the difference.

In addition, many people can't wish away anxiety. They have medical conditions that cause it. They need medical help, not platitudes.

1) Wikipedia, Serenity Prayer