Reversing settlements from a closed period

Can we reverse a settlement done in previous period which has been closed? Will it effect the P&L? Lets it can...

be done and it don't effect my previous period P&L, shall we use the same period that has been used during the settlement to reverse it even though we are in the different period now?

Reversing a settlement usually involves reopening a closed period ... And unless there is some major disaster that's not a good idea. Just based on the information above, I'd recommend asking your BASIS people to do a full client copy so you'll have a place to do what is needed without affecting the Production environment. Use the copy to open the period, reverse the settlement, and look for unintended side effects. If everything works out OK in the copy, then try it in Production if everyone is comfortable with the risks and rewards of opening a closed period.