Technically you don’t reject the contract because you may either:
a) edit 4 important contract conditions: buyer protection time, due date, fee payer, and payment amount;
b) reach out to buyer/seller via the Contract Chat, decide on new terms, create another contract and approve it.
The other party will see changes made to these conditions in the Contract Chat and should approve them. If disagree, the terms can be edited again and again until both sides approve them.