Dear Amruta Giri,
Rome was not built in a day; similarly, do not expect it to happen in a day. As per your posting, the candidate is new, and definitely, one would take time to reach the target.
Assessing the Target
In general, everywhere, the target is always fixed at a higher site. You need to analyze whether the target is not superficial and also check what the earlier target remained. It is required to calculate the shortfall percentage to the target.
Options for Improvement
If you do not wish to hire a new person, then there is one option left: give some more time. The candidate may be lacking in boosting. Call the candidate and ask him to explain what difficulties stand as hurdles. It all requires an assessment to sort out the problem and do not assert that a new one would do the miracle.