As we have noted, the Arsenal that played in the last two-thirds of the PSG game was different from the Arsenal that played in the first part of that match. The tactics changed, the confidence grew, tackles were won, territory gained and Arsenal dominated possession.
Now with a bit of luck, and with Partey playing, this tactic can be developed further. That combined with the way Odegaard changed his approach later should help Arsenal nullify PSG and then get the needed goals.
The prime disadvantage Arsenal have had this season is that of endless injuries across the team, which restricts specialist responses to specific teams. That run of injuries surely must be ending now, and this will see Arsenal progressing once more.
In short Arsenal need to play the game as they want, and stop PSG dictating play. And this should come as a surprise to PSG who are of course are used to dictating all games they play in their own league, which as we have noted before, they win year after year by massive margins.