Question about selective adjustments in Lightroom mobile

I just watched this video tutorial on Adobe's website on making selective adjustments in Lightroom. The instructor demonstrated using the eraser tool to remove parts of the mask he had created with the gradient adjustment tool, and using the brush to add to the mask.

On my iPad, I see that I can erase parts of the gradient mask I've created, but I don't see a brush to add to the selection. Is that functionality missing from the mobile version of LR?