In truth, for that connector, there is a tool, that one one end slips over the retainer to release, and on the other end, it has a split cylinder that you can slip over the wire, but it applies pressure to the back side of teh pin to get it past teh retainer. The part does not come with the tool, and it is possible to do the job without it, but it ain't easy. Be careful not to flex the wire too much so it breaks in the insulation, or pulls out of the pin/socket. You might try a moderately sized paper clip, straightened, to apply pressure to the back side of the pin.
Be careful. Don't settle for anything but a positive pin retension, or it will pull out at some inconvenient time.
Good luck,
Rich P