Managing profit and loss on corporate bonds - Germany

I maintain a basic report on a portfolio of corporate bonds, including mark to market and accrued interest. Recently, some of the holdings have been sold off and I'm unsure how to realise profit and loss without changing the average purchase price and affecting the unrealised P&L for the remaining bonds.

Very grateful for any tips; however, I'm a novice so hit me with too much jargon and you will unfortunately be met by a blank stare.

you'll need to adjust the average price for the remaining position to account for the P or L taken. If you don't you need another column for realized P&L.

Thanks for your help, wigwam!