Company A can't directly increase the pay of workers at Company B. But A can increase the pay of it's own workers, making it more desirable than working for B. The increased competition on the labor market requires B to raise their wages as well. All workers win.

The equilibrium may still not end up with A and B paying the same, but personally I care more about everyone having enough than everyone having the same, so even unequal wage increases are a positive in my book.