1. Using Processing
Give new users an easy interface to work with. One that is not as scary as the serial monitor.
We have a video that shows the process
2. Using desktop App by @Jason Snow
Try this desktop App it will ask you to install .NET Framework 3.5
It is like the mobile App but on your PC using USB to send all commands
3. Using Otto Blockly with the calibration block
The most simple way so far but annoyingly need to reupload the code until by iteration you achieve the right alignment of the motors.
It is a default example in Otto Blockly ready to open
Change the legs and feet values gradually with small values and increments(+5 or - 5 degrees)
Iteratively you have to check/upload the code multiple times, until Otto legs and feet looks completely straight.
Read this article for more details: https://www.ottodiy.com/blog/calibration
4. Using Otto Blockly with serial monitor for assistance and adjustment
I just made this "basic" example of how to quickly calibrate Otto servo motors, we have seen very good methods here with Arduino IDE, but this one aims to make it simple for beginners.
Just open/upload then start serial monitor and follow the instructions.
It is very handy because is fast and easy to leave your Otto perfectly calibrated in one upload.
But It needs improvement and actually, I found out we are missing blocks for it so we will need to create new blocks just to make this example work,
missing on variables int8_t and uint8_t
need Otto._moveServos(10, array variable); block
5. Using Arduino Serial has been always the way to do it
Upload this sketch OttoDIYLib/examples/calibration upload the code, then open serial monitor and follow instructions. But is quite advanced process for many, even do with a proper tutorial is not that hard.