Gala won the first-leg of their round 16 tie 1-0 thanks to Mario Lemina's goal.
Okan remarked afterwards: "The score was similar to the first match, but the game wasn't like the first one.
"Liverpool is a huge club, full of quality players. We did what we had to do here. We won. But it's not over. The second match is at their home ground and another very difficult match awaits us.
"Playing against a team like Liverpool is always very difficult because they are a high-quality team and you feel they can capitalise on every mistake you make. Now we will focus on the big test ahead. I always have faith in my players."
Meanwhile, matchwinner and man-of-the-match Lemina also stated: "I am grateful to my team-mates and all our fans. We wanted to win by fighting hard, just like in the first match (in the league phase).
"And we did. Now there is one more match, at Anfield. We want to win there too, we want to reach the quarter-finals.
"This is my second spell at Galatasaray. Leaving was painful. I'm so happy to be back here now, living my dreams. We're doing well in every competition, and I want to continue that way."