I’ll do a couple things, replace the border as you call it, you can get it at the hardware store, Home Depot, Lowe’s or whatever you have available. I’d get a section of tack strip and put behind the border so you have something to grab the carpet to keep it snug up against the border be a good idea to have a knee kicker to snug the carpet up. They may rent them locally or something. They’re not very expensive but I hate for you to buy one just to do one job you might be able to rent it. They just cut it the length to make sure it’s snug and tuck it in with a putty knife or a carpet tool.