While they lost the second-leg 2-1 at home on Thursday night, Forest are into the round of 16 4-2 on aggregate.
Pereira commented afterwards: "We know that games in the Europa League - especially in this phase - are not easy.
"I decided to make some changes to the team to try to recover energy. But if you change too much, there are risks.
"When they scored the first goal, we lost a bit of our confidence. After the penalty at the start of the second half, we started to play at our level, keeping the ball and creating chances with pace.
"In my mind, I wanted to give confidence to everybody... but we were not in a good situation. It was my decision but, even when we were losing 2-0, we started to play. Twice we had one-against-one against the goalkeeper."
On the draw, Pereira added: "I hope to face a strong team next because the teams in this moment are strong. We have to be ready to compete and move forward."