Even if a crewed spacecraft could be sent to it (honestly not that crazy given JWST's predicted lifespan of 20 years. Starship should be crew rated in 10 years at most and if not, Orion could be sent with some sort of expanded service module for the trip) the issue would be that docking to or even approaching the telescope is extremely risky.
You don't want to fire any thrusters in its direction to avoid damaging the sunshield or the mirrors, but of course to slow down at it you would need to do that at some point.
If the SSD failed and a constant connection to Earth cannot be maintained, the more realistic solution would probably be to launch a satellite to a high orbit to maintain permanent connectivity with JWST which can act as a store-and-forward relay, effectively replacing the SSD without having to actually go to the telescope.
You don't want to fire any thrusters in its direction to avoid damaging the sunshield or the mirrors, but of course to slow down at it you would need to do that at some point.
If the SSD failed and a constant connection to Earth cannot be maintained, the more realistic solution would probably be to launch a satellite to a high orbit to maintain permanent connectivity with JWST which can act as a store-and-forward relay, effectively replacing the SSD without having to actually go to the telescope.