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.
Standard Catalog of Smith and Wesson
The Wesson part of Smith and Wesson.
Smith & Wesson was founded in 1852.
Horace Smith, Daniel Wesson
Smith and Wesson will tell you if you call them