There will be future post about creating simple slack bots in python and this quick post is kind of related ;)
Case is quite simple, we have a bot and it produced lot of crap on several channels. Here is a simple python snippet to find and delete messages.

# -*- coding: utf-8 -*-
#!/usr/bin/python
import time
from datetime import datetime, date, time
from slackclient import SlackClient

test_chan = "development"
SLACK_TOKEN = os.getenv("SLACK_TOKEN")
slack_client = SlackClient(SLACK_TOKEN)

def get_chan_id(channel_name):
    """Get channel id"""
    channels = slack_client.api_call("channels.list")
    channel_id = None
    for channel in channels['channels']:
        if channel['name'] == channel_name:
            channel_id = channel['id']
    if channel_id == None:
        raise Exception("cannot find channel " + channel_name)
    return channel_id

def find_and_delete(start, stop, chan):
    """Find and delete messages for user"""
    oldest = (time.mktime(datetime.strptime(start, '%Y-%m-%d %H:%M:%S').timetuple()))
    latest = (time.mktime(datetime.strptime(stop, '%Y-%m-%d %H:%M:%S').timetuple()))
    history = slack_client.api_call("channels.history", channel=get_chan_id(chan), oldest=oldest, latest=latest)
    x = 0
    for i in history['messages']:
        x = x + 1
        if i['username'] == 'username':
            status = slack_client.api_call("chat.delete", channel=get_chan_id(chan), ts=i['ts'])
            print("Run: {}").format(x)
            time.sleep(5)

if __name__ == "__main__":
    find_and_delete("2019-10-26 06:00:00", "2019-10-26 08:40:00", test_chan)

Remember about slack api rate limits!

Rate Limits

Learn how to build bot users, send notifications, and interact with workspaces using our APIs.

SlackSlack