Well, not "repairing" in the traditional sense, but (re-)connecting two sections.
Briefly: for my 16x32 oval pool I cut my solar cover in two equal portions, and have been using the DIY roller concept HERE
Now I'm thinking I'll give a regular solar cover reel a try, and to avoid buying a whole new cover I would need to attach the two currently split sections and make it one big piece again. How might I do that? The cut is a straight line about 16ft wide, it's a 12mm cover.