There are a lot of youtube videos out there on how to make a custom cover for your sewing machine. Here's a link to Laura of Sew Very Easy,
https://www.youtube.com/watch?v=J0sXFuLNkR4. She usually has good instructions. I just take a rectangle of fabric, cut it a little wider and longer than I need, hem it up on all four sides and tack the sides together to make a quick dust cover for all my sewing machines.