@carusoswi: People in this thread are referring to the “perspecitve correction” module (in the “correction” group) for the automated perspective correction. For manual correction, @bastibe and @europlatus mentioned the “crop and rotate” module (in the “basic” group). You can find both by doing a search (or in your “favorites” group, if you favorite both of them in the ☰ menu for each module).
Be sure to read the “keystone” section of the “crop and rotate” module docs to learn how to manually adjust the perspective!
Additionally, the “perspective correction” module’s docs has some good info too.
Really, all the docs for darktable are great! It’s worth spending some time there. They’re organized so that looking things up quickly works well too. Sadly, they’re out of date on the official site (stuck at version 2.4), but most of the modules are similar enough.
Thankfully, a preview of the 3.0 docs are at “darktable 3.4” in the darktable usermanual and there’s an effort underway to bring the up to darktable 3.4 @ documentation · GitHub
I’ve read that there’s a goal to have up-to-date docs finished for the 3.4 release, which is scheduled for Christmas — just 69 days away from today!