Somewhere on this board there is a
jumper that I need to cut (or solder together) and change the address of one of the sensors.
Is it between the copper pads that can be seen on the photograph or elsewhere on the board?
(I don't want to scratch off the wrong conductor.)

I have two BME280 sensors and a third one - Si7021.
All three should work off the same I2C bus at the end.
One sensor will have a 0.5M cable, another one a 1M cable and the third one 1.5M cable.
Do you have any suggestions on how to make it work better?