You wil have to call S&W with the specifics of your 629
Send it to S&W or find a gunsmith.
Via the screw.
Best left to a gunsmith
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.
You can get a owner's manual for free at the S&W website
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.
A shotgun made for Smith and Wesson, sold under the Smith and Wesson name.
The Wesson part of Smith and Wesson.
Standard Catalog of Smith and Wesson
Smith and Wesson will tell you if you call them
Horace Smith, Daniel Wesson
Smith & Wesson was founded in 1852.