Hi,
There is no "Full Auth" and "Pre Auth" in the WorldPay Business gateway plugin in Hikashop as far as I can see.
So I'm not sure what you're talking about.
If it's a setting on your WorldPay merchant account, I would recommend to check with the WorldPay support.
We actually didn't develop that payment plugin. It was developed by a third party developer and given to us 8 years ago. So we actually never tested/used the plugin ourselves nor do we know how the merchant account interface looks like. We're just maintaining it so that it continue to work when we modify HikaShop (it happened once several years ago) or to add a small things, like more debug.