Hi Alysha! If the crack is thin I would fill it with a little wood putty (wood putty comes in different shades. You can buy the color that matches your stair color the best.) You can also use a wood stain marker once you have the crack filled to match the existing color of your wood stairs.
It depends on how large the crack is and the position. You can remove it, glue it and hold with clamps until dry, then replace. The wood putty suggestion by Megan will work. I would make sure you follow her tip of getting it in a matching shade. In my experience, wood putty does not take stain once it is dried.
PRY OPEN THE CRACK AND PUT IN SOME GORILLA GLUE MADE FOR WOOD AND THEN CLAMP TIGHT UJNTIL IT DRIES..
Hi there, this piece has a few solutions. https://homeguides.sfgate.com/repair-indoor-wooden-stairs-63871.html
This Old House has some directions:
Use tapered bit to drill three holes into the edge of the cracked stair tread. ...
Pull on front edge of tread to open crack.
Inject carpenter's glue into the crack, then wiggle tread to work glue down into crack.
Smear glue onto tapered dowels, and then tap them into the holes with a hammer. Then restain or paint
Do you have a picture of the crack or know how it happened? If it happened over time, you need to secure the tread with epoxy or glue. I used this kit on mine: https://amzn.to/3aLt4oD
Wood glue works, but I prefer this glue as it bonds to all surfaces: https://amzn.to/36y1Ga8
Then, fill the crack with matching wood filler like this one: https://amzn.to/2RPpQaW
Hope this Helps! Jeremy - https://do-daddy.com
Use wood glue to close it nicely and then some paint on it.