Imputation credits

So I have shares in WES.ASX that have dividends reinvested. The Imputation credits are not being auto calculated - they show as zero when I go to confirm a dividend, so i have to retrieve the div cert and check the imputation credits and manually enter the info. Is there a way to manually adjust the holding to auto apply a 30% imputation credit. I tried setting the Holding Settings - Foreign withholding tax rate to 30% but its doesnt affect the existing dividends waiting for confirmation…