How make discord.ext.tasks send in channel by id every x minutes in cogs

bot.get_channel method retrives channel from cache. You can properly do it only after on_ready event:

class Test(commands.Cog):

    def __init__(self, bot):
        self.bot = bot

    @tasks.loop(minutes=1.0)
    async def test1(self):
        channel=bot.get_channel(927612404056092702)
        channel.send(mensagem)

    @commands.Cog.listener()
    async def on_ready(self):
        if not self.test1.is_running():
            self.test1.start()


def setup(bot):
    bot.add_cog(Test(bot))