What to do if you become a manager of department where there are some employees who do not fit in your team? Their presence will harm your plans.

First give them a chance by offering training and development courses to enhance their skills in the needed areas.

Then provide on the job coaching to make sure they are qualified now and able to do the job.  

If after all this, they are still an issue then relocate them internally in the company to join another team where their skills are needed.  If that didn't work then you have to fire them.

But from the very beginning you have to make it clear that you are working with them to make them able to do the job and that if they fail they will have to leave.  You have to be fair and not just get rid of them because you don't like them.  They have to be given a fair chance.

First try, second warn,  if they didn't change their behaviour then transfer them or terminate. 

I HAVE TO DECIDE WHICH PLACE HE IS CAPABLE THEN I WILL SWITCHOVER HIM THAT DEPARTMENT AND ALTERNATIVE WILL BE SELECTED FOR MY DEPARTMENT WHO IS FIT AS WELL AS CAPABLE

I echo with the answer of Ms. Doha Shawki.

I will give them a suitable grace period to find other job if they don't fit in my team.

Otherwise I'm cheating them and cheating my self.

He/She is a part of your team. If the particular person is not fit according to your specific needs/role, the gap needs to be evaluated first. The gap can be due to lack of Knowledge, Skill or attitude towards the task to be performed. If the gap is due to Knowledge and skill, the gap can be filled with proper training. If the issue is with the attitude of the person towards the task then there is a danger as the person is willfully not able to take up the task. Organizations need to take a call on such employees as they are a potential danger to organization as they divert the enthusiasm and motivation of other employees 

Try rotating their jobs, or Try engaging them indifferent recreational and counselling activities and if still they don't change their attitude so FIRE them or Lend them to any other department if possible. 

many thanks for your invitation.

Business is Business.

But always there is a humane way to deal with such cases, i know  it's very difficult because you would like to strike a balance between business requirements and feeling human

Any employee in any Organization is retained for some genuine reasons.  Be kind enough at his good part of the works as he is good at some work. Make him happy entrusting him more responsibilities on his specialties and explain him  the importance of the current assignment with a special team in which more contributions are required by exclusive skills and the company not in a position to accommodate more than a specific number for the assigned tasks.  Anyway he should not have the feeling of being purposefully separated from the task.

Identify their strengths and assign them tasks where they can showcase their strengths. 

Give them timelines for completion. Provide them suitable training to help them complete these tasks,

If you still find them under performing then you need to either transfer them to a different department or put them in a Performance Improvement Plan.