Add custom field and fetch data from another page of zoho CRM

Add custom field and fetch data from another page of zoho CRM

Hi,
  I am new in Zoho CRM.
I have created a new event under Activity. In that form I have added one custom field called Room name. The type of the field is pick list. Now I need the value of the pick list will come from leads. All the leads name will be showing in that drop down field.

Is it possible to do this?
Please help me. Thanks in advance.