You can get a owner's manual for free at the S&W website
Via the screw.
Best left to a gunsmith
If you go to Smith and Wesson,s sight they should have a service booklet that was issued with this handgun showing proper dis assembly and cleaning procedures.
You wil have to call S&W with the specifics of your 629
Send it to S&W or find a gunsmith.
S&W, e-gunparts.com, Brownell's
You have a fixed sight K frame. You will have to call S&W to find out the exact model.
The smith and Wesson model 27-2 was made from 1962-1981.If you have a letter N prefix to the serial number,then this was started in the year 1969.If your Smith and Wesson has the target trigger,target hammer,and a partridge front sight on a 6",or 8-3/8" barrel and Goncalo Alves grips then thase were introduced in 1975.
Try Numrich gun parts corp.go to there web sight and then look up the model you are interested in,they should have a exploded view of your Smith and wesson.
press up on rear sight and top will swing up ejecting the shells.
adjust rear sight up for distance
There are no after market parts available for these guns and so a gunsmith would have to adapt something. Mounting a laser sight might be easier.