To whitelist PC in barracuda you have to create a JP Subnets/Groups. To do this you have to go to USERS/GROUPS > IP Subnets/Groups and create a Group Membership by IP. You put in the address and the netmask for a single address is 255.255.255.255. IKt wouldn’t hurt to put in the name of who this is for. Once you have that configured go to BLOCK/ACCEPT > Exceptions.

Action: Allow
Applies to: IP Group. Then select the group you made
Exception Type: All Web Traffic

Everything else should be find left default