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

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

NameTypeDescription
namestringSticker set name.
custom_emoji_idstringIdentifier of the custom emoji from the sticker set, which will be set as sticker set thumbnail; pass 0 to remove the sticker set thumbnail.

More details on telegram's documentation.