OK, but neither board has a pin labeled "DTR".
Anyway, I recommend you try manually resetting the Pro Mini in case the auto reset circuit isn't working.
If you don't have an auto-reset circuit, you'll need to manually reset your Arduino during the upload. When you don't have that auto-reset, and are resetting manually, you need to get the timing right. If you press the reset button too early, the bootloader will have already timed out by the time the upload starts. The tricky thing is that when you press the "Upload" button in the Arduino IDE, it first compiles your sketch before starting the actual upload. So you need to wait until after the compilation finishes before pressing the reset button. The way to get the timing right is to watch the black console window at the bottom of the Arduino IDE window. As soon as you see something like this:
Sketch uses 444 bytes (1%) of program storage space. Maximum is 30720 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
press and release the reset button. The upload should now finish successfully.