Mauricio Pochettino’s side failed to overturn a 3-0 first-leg deficit in front of their own fans, slipping to a 2-1 defeat against their Bundesliga opponents at White Hart Lane.
Pierre-Emerick Aubameyang scored both goals for Dortmund, who progress through to the last eight of the competition with a 5-1 aggregate victory.
READ MORE | Mature Kane can handle Euro 2016 – Pochettino
And Dier has urged Tottenham to put their exit behind them and switch their attention back to domestic matters, where they trail league leaders Leicester City by five points with only eight games to go.
"It was always going to be difficult after the first leg. We needed to score early," the youngster told the club’s official website.
"They're a very good side, but we feel we could have been better over the two legs. We move on to Bournemouth now.
"We will have to match them for energy and effort on Sunday and hopefully our quality will take over."