Let it simmer for a few minutes with the paintbrush in it. You may need to do another vinegar boiling session and comb the brush again to get it back into shape. Place it upright in a jar and reshape the bristles. After it's completely dry, store it away.

TL;DR in Indonesian:
Didihkan cuka di atas kompor. Ulangi sesuai kebutuhan. Biarkan kuas mengering dengan sendirinya.