If you've already handled everything with Tarek, there's no way to go back again. However, depending on how much farther along in the game after that you are, in the Ren'Py pages for your save files there should be the usual 1, 2, 3, 4, for pages to navigate to. There
also should be an A option, which is the game's autosaves page. This is automatic in Ren'Py, I believe. So you should be able to go to that and see if anything before Tarek is available to load. If so, you can replay that part and get the scenes from there.
Also, note that these unlocks are persistent, so if you get them starting a new game
will not remove them from your gallery. You might want to go forward to a certain point anyway (maybe Page 25 of saves?) and start a new game again.
ARLENA
That last Arlena scene is unlocked
in the middle of the nighttime. Even though you've unlocked the last two scenes in the first row, you need
to keep raising her affection by delivering her more gems. Whenever possible, choose the Should we indulge in some... stress relief? option when visiting her. That continues to raise her affection, and I believe it might be the only thing that will keep doing so. So repeat that many times (I just did that in between doing other scenes with other girls, like Ves or Divine) and you'll eventually get a new scene.
NIJAH
Note, however, that there are
more scenes below what your screenshot shows; scroll down with your mouse roller to see the additional ones available and what you may have already unlocked with those.