The gap in question was previously filled with either fiberboard or concrete crack sealant but enough of it has deteriorated to conceivably allow moisture in.
Seal gap between concrete floor and wall.
Typically this will be cracks in your foundation.
Fill the crack with urethane caulk similar to what you would use for driveway caulk.
Slide the flat end of a pry bar between the baseboard and the wall.
In the short term a sealant applied along this gap between your basement floor and wall may prevent leakage.
However it will eventually fail in one of two ways.
To remedy this issue i installed backer rod in the gap that i then covered with concrete crack sealant.
Snip the opening of the tube at a 30 degree angle making the opening the same size as your gap.
After the walls have cured the basement floor is poured leaving a similar tiny gap known as the cove joint between the cured walls and newly poured floor.
Even so the new concrete does not bond with the already cured footings so a tiny gap exists between the two.
The water being blocked by the sealant will find another gap in your foundation to enter the home.
However it s not that simple.
Use a smooth even motion filling the crack flush with the surface beveling it if it s against the house.
Remove the baseboard if present to expose the gap between the subfloor and the wall face.