It'll need to be replaced. I mean, you could try gluing it and see how you get on but I doubt it would do much good. If you want to replace it, the best bet is probably to bring it back to the shop. If they are nice, they might do it for free, though there may well be a (fairly small) charge attached.
Shops can take weeks to get all this done so be prepared to be without a cag for a while. Alternatively, you could send the cag to Nookie directly yourself - I dunno if this is any faster or cheaper (though the post alone will probably make it more expensive)
All this hilights a good point: I dunno how you ripped the wrist seal but laytex (as we all know from another use it has) is notoriuosly easy to tear. If you are getting a cag with dry, e.g. laytex seals, you should try yo get one that has a second seal over the laytex. The outer seal (usually made from neoprene) is much tougher and protects the laytext from thorns, branches, flailing finger nails, etc. Cags like this are normally a bit more expensive but worth it in the long run.
Cheers
Carlito