guntech is telling you most of it, but there's a bit more to it.
Repairing that crack and hoping to make it disapper isn't impossible but it will not be a ''quick fix"
I did one recently on one of my own rifles and as guntech says, the whole stock had to be refinished to cover it up, as the factory finishes are next to impossible to duplicate by an amatuer and I'm not good with wood.
When I repair a crack such as one shown in your picture, I find a way to duplicate the pressures that caused the crack to happen but in a much gentler manner so that I can open the crack to get glue all the way into the crack.
I don't like the runny ''super glues'' as they always leave a ''dark'' stripe along the crack, sometimes quite noticeable.
I use ''Gorrilla Glue" by adding water and mixing it together until it becomes quite viscous.
Then I use a sponge to force water into the crack while forcing the crack to widen enough to allow the water in.
After I'm sure water has reached deep enough to cover the area exposed, I start forcing the watered down Gorilla Glue into the crack as far as it will go.
Forcing means that you have to put on some disposable rubber gloves, dab glue on the tip of the finger and push it down from the top into the crack and keep on doing this until it comes out at the bottom.
You can't take time to go for a coffee or scratch your butt while doing this. Gorilla Glue starts to adhere and harden quickly. You've got five minutes or so to get enough glue into the crack before you clamp it with a soft jawed clamp.
Let it sit overnight to cure and in the morning you will come back to a stock that's as strong or stronger than new but with a yellow foam line from the Gorilla Glue expanding out of the edges of the crack.
This is a good thing because that means it worked as long as you made sure there wasn't any oil or dirt in the crack. Gorilla Glue gets it's strengh from it's expansion ability to work its way into all of the crack and soak into the wood itself and becoming part of it.
There may be a very thin blonde colored glue line but it's very easily covered up when refinishing the stock.
Most people don't bother to do much if any refinishing if they intend to keep the rifle for personal use.
The stock on my Win M70 FWT was close to pristine so it needed a full redo to asuage my sensibilities. It's slightly different in color (darker) but the wood is quite straight with little or no figure so it looks fine to me.