Take a piece of the vinyl insert and measure its width. Order a roll of replacement vinyl insert and pull the old stuff out of the aluminum channel, insert the new stuff, attach the ends the same way as they currently are (some are screwed in place, some use silicone as an adhesive) and save the rest of the roll for the next time.
https://www.amazon.com/Camco-25202-V.../dp/B0006JLW5M Cost is about $17.00 for a 100 foot roll of 1" wide insert. Be sure to order the correct color.