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'Please write code for me' questions like this are likely to be closed by the community. I would suggest reading through the help guides and attempting something for yourself and come back when you have a specific question around the trigger, then we would be glad to help.
Sree, we do not write triggers on request, there are partners and developers you can hire to do that. But we can help you learn to write code if that is what you're trying to do. If that is the case, I suggest you update the question with what you have tried to do, where you're stuck and what your code looks like.
You can simply use an action based workflow to accomplish this. You do not need an Apex trigger to accomplish this. Using out of box features is always better than writing custom code.