Is your jacket a rain jacket or a baffled jacket (like a down jacket or Nano Puff)? The repair process for each is slightly different. In either case, you will need to patch over the whole tear to prevent water from seeping in. You may even need to sew the old material down underneath the patch.
We have a guide on how to patch a baffled jacket here: How To Repair A Baffle On A Patagonia Down Jacket
For a regular rain jacket, you can apply a watch of waterproof fabric over the top and sew it down along the edge. You will want to fold the edges of the patch under so that they are caught in the stitching. You can follow the steps in this guide for a basic patching procedure: Repairing Patagonia Jacket with a Shaped Baffle
If you need additional help you can contact Patagonia customer service.
Good luck and let us know how it goes!