OK so we know the trouble so no shooting is involved but the post also asked for a fix if possible.
You can't do anything useful with just a screwdriver. You will need some software tools.
If by format you mean that the partition table was altered so that no partitions are defined then it may be possible to use a utility like fdisk to recreate the partition and reboot to see if the file system shows up. (Sun OS/Solaris uses a utility called format to create partition tables.) So you would need a bootable floppy or CDROM with a compatible fdisk utility.
Otherwise my advice is to stick that screwdriver where the Sun never shines, and by that I mean inside the floppy disk drive, and then reboot. :D
Or just walk away. The client isn't going to be happy no matter what you do so just get the heck out of there and don't look back. Don't let the door hit you on the way out.