Once you have added an other asset to the system, you can set whether it is single or joint.
Navigate to Clients> Holdings> Other assets:
Next to the other asset you will see the following icon:
This indicates the asset is single.
To change the asset to joint, click into the asset and select the person icon, as seen on the screenshot below:
Select 'I> Change the ownership of this asset'
Select 'Single' or 'Joint'.
For this example, I will select 'Joint'.
Once you are done, click '<I Return'
You will now see the icon has change to show joint ownership: