The best way is to use the Captains Mode. Bots will automatically follow functions and lanes based on the order of picks (in Captains Mode):

1th pick: Offlaner (hardlane)
2th pick: Soft-Supp (hardlane)
3th pick: Mid (midlane)
4th pick: Hard-Supp (safelane)
5th pick: Hard-Carry (safelane)

So, if you want to play as a hard carry, for example, choose your hero in the last (5th) pick of the CM mode.
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In other game modes, you can enter the names of the lanes in the chat to change the bot lanes (from left to right). By default, bots follow "mid, top, top, bot, bot" order — and as you will always be in the first colors of each team (blue or pink), you are configured as midlane by default.

After you and the bots choose the heroes, you can enter the commands mid, bot or top for each hero.
Example: top, top, bot, bot, mid (here you will go to the top lane — first color, ever!).

P.S.:
1. You have to enter the lanes in the chat BEFORE the game starts.
2. Go to the lane you chose before the first wave of creeps left the base AND STAY IN IT (on the trail), otherwise another bot will try to steal your lane.

Still talking about the other game modes:

Ah, I forgot to say that you don't need to put commas (,) when typing lanes. You just need to have a space between the words.

Thank you, Doctor.

I will give this a try.

If this works I will be even more grateful than I am already for the quick response.

PS: Is there a place where this is documented so I can refer to it later? other than your reply i mean?

Thanks again.

Update: 23 Sep, 2017 @ 11:32pm
Take a look at Update: 23 Sep, 2017 @ 11:32pm changelog. It won't work for IO and ET though

thank you for all the advice.

my only other request/question is a way to pick which heroes the bots will pick on the other team?

I've found the hero_selection.lua file and after looking around it appears the 'local requiredHeroes' is what I might be looking for but I'm not exactly sure how to do this or if it's possible.

captain's mode, two human players on one team and the rest bots.

if we want to practice a duo and draft accordingly, with the order, how do I make sure the bots pick specific heroes we are wanting to lane against?

Thanks again for the help, the updates, and the script. it's great.