The claim is not supported by the specification. If you feel that it is not supported yourself, you can modify the claim and narrow the scope of the claim to make it supported by the specification. This lies in your ability to summarize the instructions.
If you feel that your claim can actually be supported by the instructions, but it is not obvious enough, you can try to convince the examiner by replying, which depends on your ability to reply.
If it is not done properly, it may be rejected. However, not every patent will be rejected the second time. One patent we represent was notified four times during the actual trial (due to lack of novelty and creativity), and we finally gave it after many times of defense. So, first believe in your own plan, believe in your own ability and try to defend it.
after rejection, you can apply for a review.
if it is an invention, it has been made public before the actual trial, and after it is rejected, you can't submit an application on the same subject. What has been made public before has already constituted the prior art..