Are you talking about the circular type of "screwdriver" that looks like a metal washer with a hole in the middle? If you go to your dealer, they will probably give you another one. A regular flat blade screwdriver will work well too; just look for one with a blade that fits the screw slot relatively well. Good luck!!
You can also buy stumpy (very short) screw drivers at tool & auto shops which might be easier to grasp than the small tool they provide with your machine (mine machine ones are either oval metal discs or a weird T shape). I've also used a coin to remove the feed dog plate in a hurry lol :) xXx
I am sure a quick call to you dealer would work..they probably have one or could order you one for a minimal charge...
Look in your sewing machine manual for the item name and part number then go on the makers website for replacement tools. I think it called a round disc screwdriver