how to use If and then statement to copy from ones sheet to another

I am using this if statement to compare the value on C1 on two tabs and if the value are the same copying the value on F1 on sheet1 to F1 sheet 2. But i want to add a statement that if there is a value already on Sheet2 F1, not to replace it but to add it and separate with a coma.

 =if('Original list'!C1='Second list'!C1,'Second list'!C1,0)