If you pay for a year of business hosting up front, they’ll likely do it for you. If not, as you say, there is a script for that. You run that script like the others (so find any other guide for running an import script), so you’ll need a working Discourse to run the job on. After you do that, you make a backup, upload it to your site, and ask the Discourse folks to restore it.
This will erase all of your data in Discourse. If you haven’t launched your site yet, this is no problem. If you have data on your Discourse site that you don’t want to lose, then it’s a much more complicated game.
If your site has data that you want to keep it’s more difficult. You’d need to freeze the site, make and download the backup, run the script on your machine, backup and upload it to them and then have them restore it.
If you can’t afford a year of business, you can post your budget in marketplace or ask me (or see Discourse Migration - Literate Computing).