Getting your old data out of Discourse
First you will need to retrieve a copy (database dump) of your current forum, which you can then import in Playgroup. To do that, go to you Discourse admin panel and create a new backup. Depending on the size of your forum, this might take a while. Discourse will usually notify you by email when the dump is done, giving you a direct download link to your newly created backup. You can also always go to your admin dashboard and download dumps under the backups tab.
Preparing to upload
Now that you have downloaded the whole backup, you need to extract the relevant SQL file, so you can upload it in the next step. If you're on a Mac, simply double click the (.tr.gz) archive to unpack it. Windows users can resort to 7Zip for example to unpack the SQL file.
Upload to Playgroup
Once you have unpacked the dump.sql file, you can go to your admin dashboard and from the left side menu select "Import Content". There you can upload the extracted SQL file, which will then be imported. You just have to select the file and click "Import content" for the import to start. The process might take some minutes, depending on the size of your forum. Once the import is done, you will see a notification and all your content should now be visible in Playgroup. All existing users are now whitelisted, which means they're allowed to create an account with our private community, by singing up through your regular login page.