Copy one field to another in the deals module

Copy one field to another in the deals module

Hello - I am trying to do something that is really simple, but I am completely stuck on how to do it. Since Zoho CRM does not allow you to create a formula field that gets a value from another formula field, I have created a dummy field to hold the value of the initial formula field so that I can use that instead. So basically, I just need code for a function that copies the value in a field named Total_Costs and paste it into a field called Total_Cost_Hold_Field. I can create the workflow rules to update the field. I am just unable to figure out the code to copy and paste the value from one field to another. Both of these fields are in the Deals module. 

Thanks in advance!