tracked_channels = []

@client.command()
async def track(ctx, channels: commands.Greedy[discord.TextChannel] = None):
  global tracked_channels
  tracked_channels = channels

@client.event
async def on_message(message):
  await client.process_commands(message)
  if message.channel in tracked_channels:
    await message.add_reaction('\U0001f983')

@client.event
async def on_reaction_add(reaction, user):
  if reaction.message.channel in tracked_channels and reaction.emoji == '\U0001f983' and user != client.user:
    await reaction.remove(user)
    await user.create_dm()
    await user.dm_channel.send(embed=discord.Embed(title="HAPPY ONE DAY BIRTHDAY, JACOB!! :partying_face:", colour=0xE94545, description=f"Happy birthday to you.\nHappy birthday to you.\nHappy birthday dear Jacob.\nHappy birthday to you.\n:turkey:"))