Hi Sourabh,
It depends on if you just want to reverse the specific flow or the whole transaction.
For a specific flow you may go to FTR_EDIT change, goto cash flow tab and reverse mode as the following screen:
And then you can right click the flows to reverse it and save.
And then goto TPM10 to post the ToR flows.
And for the whole transaction, you can just run FTR_EDIT->Reverse to reverse it.
And then the same, you need to run TPM10 to post.
Regards, Feng