Capital return how to process

I had a capital return during the tax year and have tried to process it a number of ways but its still not working correctly.  I want to increase the bank account balance as it was funds received but reduce the cost base of the investment.   The capital return option I have chosen keeps on increasing both the bank account and asset cost.  Even with a negative sign in front doesn't get the right result.  Does it need a 2 step process?  I can't find any history of answers on this despite it being a common corporate action. Someone might be able to point me to an earlier post with the answer.