Telethon script to delete all messages from a certain channel/group/user.

delall.py

from telethon import TelegramClient
from telethon.tl.types import PeerChannel
import asyncio

api_id = xxxxxx # Replace with your API ID.
api_hash = 'your_api_hash' # Replace with your API Hash.
getting_entity_ID = 'publicgroupusername/publicchannelusername' # No @ symbol, enter username only.

client = TelegramClient('session_name', api_id, api_hash)

async def delete_my_messages():
    await client.start()

    entity = await client.get_entity(getting_entity_ID)
    me = await client.get_me()

    async for msg in client.iter_messages(entity):
        if msg.sender_id == me.id:
            try:
                await client.delete_messages(entity, msg.id)
                print(f"Deleted message ID {msg.id}")
            except Exception as e:
                print(f"Failed to delete {msg.id}: {e}")

    await client.disconnect()

asyncio.run(delete_my_messages())

If you're using IDs, you can delete line 7 entirely and replace "getting_entity_ID" in line 14 with your actual ID.
For example, if the ID is 7005674652:
For a channel, prefix it with -100, like -1007005674652
For a group, prefix it with a single dash, like -7005674652
For other cases, use the ID as-is.