I haven't really used custom forms much, but I believe you will need to push (publish) the forms to the pc's you want to capture data for, then on that client pc, you should be able to launch the custom forms link from the LANDesk Management program list & fill in the info required.
If you want to manage the cost center info from the console, a better option might be to simply add a custom inventory value called "Cost Center" & enter a value for that pc. Otherwise you need to enter the cost center on the client pc itself & will need to publish the form to each new pc you want to capture it for.
To add the custom data, open the inventory for any pc, browse to where you want to keep the value, then click the "ab" button (or right-click & select "New String") I would suggest the string value since it gives you more flexibility with alpha-numeric information. Integer limits you to just #'s. Give it a name & enter a value for that pc. Then wait... Not sure exactly how long this takes to populate, but I usually do this in the AM & come back to it later in the afternoon or the next day.
Once added to inventory, you will see that inventory item on all clients & will be able to enter values for each as needed direct from the LDMS Console.