Access the option to withhold funds from an owner via the Rental ledgers page - click Trust Accounts on the green menu bar, and then 'Rental Ledger Balances'.

On each ledger line you will be able to see any amount currently being withheld, and click that amount to add more withholds or make changes.

Add a withhold by entering an amount and reason, optional to add a date for the withhold to end.

Multiple amounts can be withheld at the same time. Enter above screen; 'Add New' to withhold further funds. Select the pencil icon to edit the withhold or the red icon to delete. 

Funds may also be put on withhold during the disbursement process in the same way.