contractAddress info to deploy to mainnet

[ScRhino]

Just can't seem to get a straight answer for this after trying and searching for hours it seems several others have had the same problems with no straight answer over the past couple of months. All of the tutorials are great for launching and testing on the testnets but now ready to launch on the mainnet. What do you do with this section in CollectionConfig.ts? Do you leave the contractAddress from the testnet or do you change it back to null before deploying on the mainnet? Also, what do you put in the marketplaceIdentifier?