Once an offer has been submitted on your listing.

You can assign the offer documents to your seller or sellers to sign by clicking the Assign button.

Accepting does not execute the contract by itself. Once every signature is in place, the status changes to Executed and the offer moves out of the offer folder into the Executed Contract section of the deal.

Check the arrow on the SHARE WITH SELLER button — the two options are inside that dropdown, not on the button itself.

If the dropdown is not there at all, these actions only exist on offers that were created in Jointly. If the offer documents were uploaded rather than built in Jointly, there is nothing to accept or reject — you can only share the documents with your seller.