Bearing capacity is for the subsurface soils, a wall is a structural element which sits on a foundation exerting a pressure on the underlying soils which have a bearing capacity.
If you want to use the wall in your design you need to assess it for strength and figure out how much bearing pressure it is exerting on the soil, then ask a geotechnical engineer if the underlying soils could handle the increase.
Also note if you are relying on an old wall think lifespan and condition as someone is responsible for saying the wall has sufficient strength in the existing condition and will work with the beam.
The first stage of site investigation is desktop and it informs the engineer of the anticipated subsurface conditions. By precluding the site investigation the design engineer cannot accept any responsibility for providing a safe and economical design.