Here is the stepup converter I'm trying to use. It has multiple choice voltage output and by default outputs 12V (tested).
I want to get 5V output but I cannot make it change.
I tried sauldering A (I mean top left of the board), or A and B together but nothing changes.
How is the schema on the back supposed to be deciphered?
Those spots are a pair of pads on the circuit board. Right now they have a solder jumper across them giving you the 12 volts.
Remove that solder jumper and you will get the 5 volts you want, if the diagram is correct.
The capacitor circled in green is irrelavent.
You need to remove the 2x 0 Ohm resistors circled in red to get 5V output.
Don't worry about loosing or damaging those 0 Ohm resistors, you can replace them with a blob of solder later if you change your mind.
Do make sure you remove any excess solder after your remove the resistors, so that the pads underneath are not bridged.
