#1
message = ctx.send("text")
#2
message = channel.send("text")
#3
message = channel.fetch_message(messageid)
#add reaction to message
emoji = 'N{THUMBS UP SIGN}'
await message.add_reaction(emoji)
await message.add_reaction(emoji)
await bot.add_reaction(msg, emoji)
#react command
@bot.command()
@commands.has_permissions(manage_messages=True)
async def react(ctx,emoji,message_id):
channel = ctx.channel
msg = await channel.fetch_message(message_id)
await msg.add_reaction(emoji)