The idiom "rearrange the deck chairs on the Titanic" means to spend time and effort on something that is ultimately pointless or futile. It comes from the real-life tragedy of the sinking of the Titanic, where the crew of the ship was rearranging the deck chairs even as the ship was sinking and there was no hope of saving it.
We use this idiom when we want to suggest that someone is wasting their time on something that is not going to make any difference in the end. For example, if someone is trying to fix a broken computer by rearranging the cables, we might say "You're just rearranging the deck chairs on the Titanic. You need to get a new computer."
In short, this idiom is used to convey the idea that someone is focusing on trivial or insignificant details while ignoring the bigger, more important issues at hand.
• The politician's attempt to address the country's deeply-rooted issues with a superficial policy change was seen as nothing more than rearranging the deck chairs on the Titanic. (figurative meaning)
• The new manager was trying to improve the company's performance, but his efforts seemed futile, just like rearranging the deck chairs on the Titanic. (figurative meaning)
• The writer knew that trying to fix the plot holes in his novel at this stage would be like rearranging the deck chairs on the Titanic, but he did it anyway in the hopes of salvaging the story. (figurative meaning)
• I have to rearrange the deck chairs on the Titanic, but I don't know where to start. (literal meaning)
• My friend keeps trying to fix his failing business, but I feel like he's just rearranging the deck chairs on the Titanic. (figurative meaning)
• Despite their best efforts to save the failing project, it was clear that they were just rearranging the deck chairs on the Titanic. (figurative meaning)