Give Free Space from "Free Space" partition to a specific partition

After some issues with my internal disk, I moved my OS on an external drive which is split into : - (disk2s2) Macintosh HD (Apple_HFS): my operating system; - (disk2s5) Volume 1 (Apple_HFS): My data Storage - Free Space: A free space partition resulting in my messing up I want to give the free space (550 GB) to Volume 1 (my data storage) but the command "resizeVolume" only allows me to give the free space to "Machintosh HD" (my OS) and not to "Volume1". The issue is that since my partitions are in Apple_HFS formats and not in APFS format, I cannot use the "resizeContainer" command as suggested in other posts. I don't want to lose any data on both partitions. How should I do it?