Unai Emery's side face the first leg of their all-Spanish meeting with Atletico at Madrid's Estadio Vicente Calderón Thursday on the back of a crushing domestic defeat.
They have the consolation of retaining third spot in La Liga in the race for a Champions League place.
"We know we must improve many things between now and Thursday to arrive at Mestalla with a good result," said on-loan Real Madrid midfielder Canales.
"On Thursday we have a very important game, and most important now is to lift the head and return to the previous dynamic. Now we take a time not so good as before but still have the same attitude and commitment.
"We know that yesterday we had a bad game. Losing 4-0..we all know what we did right and wrong."
Midfielder Canales is set to extend his loan deal from Real next term.
"I'm very happy here despite not playing many games with the injury. The people have given me much love," added Canales.