"In that case, resort to DOS 6.22 (or whatever version you have already on HDs) may be necessary to first "un-lock" the drive, from whatever OS/2 FDISK won't touch."
Which may mean deleting any "non-standard" partitions (ie: any that OS/2 doesnt like, like a FAT32 partition, a greater than 2GB FAT16 partition, or an NTFS or Linux partition, or another bootloader).