Make Icons perfectly transparent

Hi,

please see the demo forum:
https://asdasd.fboard.de/
https://asdasd.fboard.de/demo-forum-1-f1.html
https://fboard.de/asdasd/asdfasdfasd-t2.html
…

All colour is black just to see only the icons. This task is not about the demo forum, it is an image task only.

The icons have the problem, that their transparency is not perfect. At the transition between transparent and non-transparent, there are some white pixels.

Target of this task is to make those white pixels transparent, without changing the size, quality, compression, datatype etc. of the image. They are gif, jpeg or png and each file must stay the type it is. Nothing else should change except the transparency of the transarent/non-transparent border to be beautiful when having dark background (and also being perfectly fine having white background of course). Just make the white pixels at the borders transparent and check each file manually against black background.
You don’t need the forum for this, you can simply show all of them in an empty html file with black background.
Goal is to deliver a html file with black background which shows all graphics, of course with a perfect transparent/non-transparent transition. Corrected graphics should be also returned in the same folder structure as sent.

There are more or less 929 icons which must be checked (most of them 1 icon set per language, 40 languages), most of them but not all of them need special threatment.

The icons belong to a free forum host. Please make proposals how you will approach this task and not change anything of the graphics except clearing up the transparent/non-transparent transition.

All icons are provided in a zip file attached. I also uploaded 1 screnshot with red arrows targeting to what I mean.

Best Regards