akaunting-select

Good evening, sorry my English is a little rusty.
Please does anyone know how I do, after selecting an item in the combo (akaunting-select) it makes an ajax request and populates another combo (akaunting-select)?
The onChange function and ajax I already got it, but I don't know how to find the other combo and fill in it options.

thank you very much for your attention

best regards
André