The Hoops experienced a rare defeat when Motherwell edged them 2-1 at Fir Park on Wednesday night but Forrest says Saturday's trip to St Mirren Park is now the sole focus.
"It's a team game and maybe in the next match I won't play well and somebody else will, so it's all about the team and hopefully we can get back on track on Saturday," said Forrest.
"It was disappointing. I felt we created enough chances to win the game, and they had two or three shots and scored from two of them so we were a bit unlucky.
"We knew that they are second or third in the league, and we were all up for the game. It just wasn't to be our night and we just need to prepare for Saturday now.
"All of the boys will be up for it, and obviously we want to win the game and go as far as we can in the cup."