Once you find a end buyer, you must decide how you want to close. If you will do a double close, then you just put your buyer under contract using a new purchase agreement (the difference between this purchase price and your contract price is your payment). If you will reassign your contract, you need to create a reassignment contract. This is a simple attorney drawn document. You may even be able to get a copy of this from websites endorsing wholesale R/E deals.
Make sure you have the correct clauses in both agreements to protect yourself and your buyers.