It is fiddly and access is tight as all the connectors are in place. However, if you approach at the correct angle so that you are looking to latch the connector next to the battery first... Once this is in place and secure then gently push down the front of the bracket over the cable.
when reassembling, getting bracket back on can be tough. There is a tiny tab which is on the top left of the braket in the picture that can become easily bent. Make sure this is at 90 degrees to the bracket so that it can slide into a small hole to the left of the camera opening, which is used to secure the top left of the bracket to the phone.