How do I replace the copper sleeve in tail end of transmission

That's a copper bushing... Since it's cutting your tail shaft seals, it should be easy to remove. To install, you can tap the bushing back into it's seat by using a large socket. Be very careful tapping the bushing in, it can get smashed if you hit it to hard.

Note: Some tail shafts have to be removed in order to install this bushing. Some of these tail shafts have speedometer gears, sensors, and clips that are a pain in the butt to get to. This may not be in your case, but just wanted to make note of it.