I had to replace the screen on a broken smartphone in the last year. To get the screen free required a nearly total disassembly of the phone itself, followed naturally enough by a nearly complete (re)assembly. Most people would consider say that smartphones are a subset of computers; one can quibble as to whether "repair == assembly."
If the intent of the question is more along the lines of "When did you last purchase components for a desktop computer and put them all together yourself (i.e., sticking processor into socket, RAM into the mobo, etc.)?" Then the answer is: not in a decade, since that was when I last had a personal machine that was a desktop that required such assembly.
As a middle ground, I changed some of the components of my personal laptop (new HDD, more RAM, new battery, replaced a finicky flex cable). That was to years ago.