You cannot replace a couple moment with a single force. That would introduce an erroneous term to the vertical force balance.
There is a reason why it is called a couple moment. If you want to replace it with forces you can do the following. Add 2 forces that are equal in magnitude, opposite in direction and do not share the same line of action such that their net moment along the axis of interest gives you the same value.
Additionally, as long as you do not change the direction of axis, you can move the point of application of moments and even combine them all with one along each orthogonal direction. Therefore, you can imagine moving the moment at point A to point B and performing the moment balance to find your reaction forces.
Be careful, however, when you try to do the same with forces. In that case, you might have to add additional moments to your equations in order to include the effect of forces on moment balance.