The Bees host Liverpool having drawn 2-2 with City thanks to late goals from Yoane Wissa and Christian Norgaard.
Speaking about his side's confidence, Frank said, "I think it was a good indicator for how even a match it was.
"Of course we will try to do the same against Liverpool.
"It will be difficult. I think for me and for us the performance was so good in terms of the way we want to do it.
"We were brave playing out but also brave in high pressure, brave in a lot of other phases, and I think we need to be brave again on Saturday."
Frank was also asked about transfer rumours swirling around Bryan Mbeumo, including linking him with Saturday's opponents Liverpool.
He added: "It would be that big a fee (to tempt a deal) that I can't imagine the size of the fee.
"I'm not even focused on keeping the best players, I'm just expecting them to stay.
"And adding? We are always in the market. We don't have urgency to bring new players in, but of course, we are aware if we suddenly need some."