New SD card partition for video/photos

[Solarbot]

Hi, I have MotioneyeOS running on a PI4 and 128Gb sd card that shows 3 partitions. One seems to hold all the files, the second I'm not sure about and the third is 100Gb and empty which is where I would like to store the video/photos. At the moment the first partition has filled up quickly as its less then 5Gb but the other partion doesn't show as a location that I can select under 'file storage'. All I can see is SDABC 0xaa000000 and custom path. Can anyone help me configure and use this 100Gb which is currently empty? I've also tried to increase the size of the first partition using Gparted in Linux but this doesn't seem to be possible? Thanks in advance.