Dortmund will face Augsburg but it seems they will not play their key players full time because of course they will save energy and ensure the players' performance remains in good condition when the second leg match takes place, because Dortmund only needs to draw to qualify for the UCL final. this season, but PSG will definitely try to score a goal against Dortmund, especially playing in front of all their supporters, of course they want to win and reach the UCL final this season because Mbappe doesn't want his dream of bringing PSG to the UCL final to be buried again because he failed for the umpteenth time. He will definitely try to play as well as possible to score goals and Dortmund must be careful in the second leg.
Dortmund has secured fifth place. They have confirmed their ticket to the European League group stage next season. I don't think Frankfurt will be able to catch up on their points. So as you said Dortmund will not play all their key players in that match. They already have a goal advantage in the first leg so I think Dortmund will not waste this opportunity. But a 1 goal lead doesn't make much difference. PSG will play aggressively to get 1 goal and I think it will not be difficult for them because they will play at home next week.
Dortmund's performance this season should have been a little better as they are playing in the semi-finals of the Champions League this season and they have a chance to qualify for the Champions League final if they beat PSG in the first leg of the semi-finals. However, this team has performed badly in this season's league tournament due to which they did not qualify for the Champions League next season and they will qualify for the Europa League next season. They needed to improve their performance enough to qualify for the Champions League again next season. They have to be satisfied with this result as they have no chance now. Now all they have to do is plan hard for the second leg match. Either way they can protect their goal post. Since they are leading by one goal, they have to keep the goal post safe because if the goal post is not scored, then their final is guaranteed.