Use the transform tool (looks like a cross, upper right). Tap it; tap and drag the handle on the right (has a circle with an arrow) clockwise or counter-clockwise to rotate. Use the crop tool after to crop the result (if you need to).
I found a method but it does require a few steps. I used the tutorial image of the old truck (one you change to sepia) for my testing.
This is the process I went through
1. Created a new empty layer at the top of the layer stack
2. Using the marquee selection tool, I drew a very thin horizontal rectangular section, essentially a line, for reference when correcting the horizon on the original image. I positioned it close to the actual horizon on the original image
3. Using the Ampersand icon menu I selected Fill and Stroke, and filled the selection with something that would contrast well with the horizon of the original image. I used a bright red.
4. I then duplicated the original background layer of the image using the + icon at the bottom of the layer stack and Duplicate Layer button and turned off visibility of the actual original background layer
5. With the newly created duplicate layer selected, I chose the Layer Move tool icon at the top (looks like a plus symbol or cross with arrows at the tips)
6. This framed the image with anchor markers with options for distorting and rotating the image. I used the one for rotation on the right-hand side (circle with arrow wrapping in on itself going clockwise) to rotate the entire image. You basically press and hold on the icon and move your finger up and down on the screen rotate. I rotated it to where it visually appeared level in reference to the horizontal reference line created in steps 2 and 3. The Old car image it ended up being negative 2.1 degrees. Hit the Done button to complete the rotation
7. Select Crop from the Ampersand icon menu; position the crop area anchor markers to have a perfectly rectangular image. I found it easier to do so when disabling the Chain icon (maintain aspect) and Magnet icon for snapping.
The process is a little involved and more work than offerings in Adobe desktop apps but it can be done. My answer is basically the samething as Warunicorn, just a little more drawn out, thought I'd post it anyway for the heck of it...