The visitors won 3-1 with two goals coming from set-pieces.
“I think that Everton deserved to win," Frank said. "The first five games we played this season, we performed very well - this was a bad performance. We need to learn from that, move forward and bounce back.
“What this group of fantastic players have done very well over all the years I've been in charge here is that, after a bad performance, they've bounced back. So I expect that will happen on Wednesday against Arsenal."
He added: "Everything that Everton came with didn't surprise us. We expected everything, we just handled it poorly. We just didn't deal very well with it.
“There are two things, besides the bad performance, that we need to look into: one is defensive set-pieces, obviously we conceded two goals and we weren't on top of them.
“Secondly, is our quality and decision-making on the ball, especially in the first half. We were throwing the ball away way, way too easy with touches, passes and decisions."