First thing you're gonna want to do is start up a mvm map via the console. (map mvm_bigrock)
after you have loaded up your game turn on cheats, as this is the only way I am aware to get this to work without third party servers. After you have turned cheats on, type this into your console twice

ent_remove_all tf_logic_mann_vs_machine;ent_remove_all tf_gamerule mvm;ent_create tf_gamerules ctf

What this should have done, is turn the game into a competitive version of capture the flag, which should allow you to change to Blu.

In order for your game to revert back to MVM is a bit complicated due to the command being out of date.
Type this into your console twice: ent_create tf_logic_mann_vs_machine;ent_create tf_gamerules
mvm

You will get this error message: Attempted to create unknown entity type tf_gamerulesmvm!

After you have joined Blu team type in this command twice: ent_create tf_gamerules ctf

(I'm not sure if it was an update, but it seems that tf2 disables the tournament mode, requiring you to type into console: mp_tournament 1)

what this should cause to happen is that it is trying to change the game mode, but will revert it back to mvm. You will sound like a robot, but you will look like a human. The only way to be a robot is with commands. There's another guide linked in the comments to help you find the commands to turn yourself into one. If you swap yourself into a robots model then respawn, your eyes will glow like a robot.

You will come to notice that now there is no red team, the best thing you can do is type in: tf_bot_add 10

You will only get ONE red bot, but if you type in: tf_bot_kick all

You will end up kicking all the bots, even in spectator waiting to be on Blu team. They will all join red. One of the only ways I know to get the bots out of the spawn rooms is to spawn a neutral intelligence. Fly over to where the robots spawn, and type in this command: ent_create item_teamflag GameType 1 TeamNum 0

This SHOULD spawn in a white intelligence, that will either make the bots come out or not. If they do not come out, kick all the bots again, they should leave the spawn rooms.

When you ready up, you will have to wait the 150 seconds, so I recommend turning up the host_timescale to 3 so it goes by faster. When the round starts, you and only one other Blu robot should spawn, if you want more, kick all the bots again, some should join red and some should join Blu.

Extra: If you use the currency_give command, you can give yourself money on the Blu team and even upgrade. Blu spies can also sap the red team.

You the player do not have the ability to deploy the bomb, you can run around with it though and lead the other robots. What you should take notice is that if the bomb gets deployed you will be forced into spectate and wont be able to start the game. If this happens or the wave is completed, kick all the bots and join red again. You will have to go back to square one.