Resolution-

1. Set Field to constant Value A is an inbuilt Function provided in Calculator Step.
   
2. It is used to assign a constant value to a variable.
   
3. In the Calculator step, we cannot directly use any data value, we need to have a value in form of a variable. So we can use this Set Field to constant value A and convert data to Variable.
   
4. To use this functionality perform the below steps-
   
1. In the new Field: define a variable.
   
2. In calculation: select Set Filed to constant Value A function.
   
3. In New Filed A: set the value which you want to assign.
   
4. In value: Set the data type.
   

Refer the below Image for better Understanding-