i typically have to use a small tapered file but i only bother on some pocketknives. That looks like a cheaper knife and i wouldn't do it unless i wanted to waste time since it would take longer than its probably worth to just buy a new one and the files aint cheap. Go to Walmart and buy a new one and make that the new garage beater. I've seen and used a lot of decent sub $1 knives at Walmart and the file sharpener is around 10 bucks or more.
Just look up tapered rod knife sharpener, tapered diamond rod knife sharpener, or serrations sharpener. I use a little smith one idk the name and the lansky blademedic and both are alright and costed about the same. i like the blade medic more.
Shop around on amazon. Just avoid the sharpening steels or honing rods, honing steel those don't do serrations. Look for those fine tapered sharpening files or ceramics.