It takes guts to admit you were wrong and this goes for nations as well as individuals.
The Germans admitted they were wrong circa 1948 and have since gone from strength to strength. (There are still a small minority of Germans who think Adolf was wonderful, but they are a tiny minority.)
The first step for us is to acknowledge that Brexit was an error. Folly. That does not reverse it, and indeed it cannot be reversed as such. We shall never again enjoy the huge privileges we had as the EU member state with the best deal of all.
But from that starting point, we need to build our way back. The hard truth is there is no realistic alternative.