Hi @DIYerLP,
Welcome to the Bunnings Workshop community, it is fantastic to have you with us.
In the current set-up, you already have rafters which run between the beam on the left and whatever is supporting them to the right of the image. You would need to add what they'd refer to as battens between these existing rafters.
In saying this, the addition of battens would only really make sense if the sheets were running from right to left, so I'm not entirely sure you need them.
The way to increase the pitch of your pergola is to remove the roof sheets, then pack out the top of the existing rafters with H3 Framing Timber. You'll want to increase the height at the top of the pitch the most, with smaller timbers being used as you move down the slope.
These timbers would need to be cut at an angle so that the roof sheets attach to them perfectly flat and in line with the desired pitch.
This work would be pretty complex and would require some fairly in-depth planning to achieve a consistent pitch. I would strongly consider having a carpenter or roofer assist with this work, as it is not exactly simple.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
