View Source ExTDLib.Method.SetStickerSetThumbnail (ExTDLib v0.0.4)

Sets a sticker set thumbnail; for bots only. Returns object_ptr<Ok>.

NameTypeDescription
user_idstringSticker set owner.
namestringSticker set name.
thumbnailInputFileThumbnail to set in PNG, TGS, or WEBM format; pass null to remove the sticker set thumbnail. Thumbnail format must match the format of stickers in the set.

More details on telegram's documentation.