This is the code that I used:
@client.command(pass_context = True)
async def music(ctx, *args):
global mesg
mesg = 'https://cdn.discordapp.com/attachments/759465899844567157/797828093494558740/videoplayback.mp4'.join(args)
return await client.say(mesg)
Nevermind it's been fixed, I had to restart the bot when I add a new command ♂️