"Their" is correct, because it shows possession of the desk by someone else.
editing
The editing stage of the writing process is when the writer typically reads each words of a draft aloud and listens for stylistic, grammatical, and other errors. At this point the writer has created a complete draft of the composition. While there have been some edits during the draft process, during this stage the writer focuses solely on editing the composition for any errors. The other stages of the writing process are brainstorming, outlining, drafting and publishing.
