To get your brushes visit https://www.grutbrushes.com/procreate-brushes/
As long as you are logged in to your account and your membership has not expired you will see all the brushes and a download link to download each one. 
1. Open that link on your iPad (choose to open it in Procreate)
2. Tap on the "download" button under the brush you want to install 
3. Choose open in Procreate (Safari) or "Share to Procreate" (Chrome)
and Procreate will open with your brush installed and ready to paint with!