On what gun?
The "Fix" depends on the brand and type.
"Usually" the ratchet is NOT the part needing attention, it's actually a combination of the cylinder and the cylinder locking bolt.
In a case where 5 chambers are OK and one isn't, it's probably a matter of that chamber's locking notch being out of spec or damaged/worn.
MOST modern DA revolvers like S&W, Ruger, Dan Wesson, Taurus, and the later design Colt's, are not supposed to lock up tightly.
The design requires that the cylinder be slightly loose in order for the gun to work properly.
The only DA revolvers that lock up TIGHT are the older Colt designs like the Python and Detective Special.