Baking Soda, Sodium Bicarbonate, is an alkaline substance with a pH of abnout 8.2. Baking Soda will not lower a soils pH. You would need many pounds of Baking Soda to make any significant change to a soils pH.
As a general rule of thumb what is available to organic gardeners to lower a soils pH is sulfur, but how much to use depends on what your soils pH is, how much that pH might need to be lowered, the type of soil you have, how much organic matter is in that soil.
If your soil needs a pH adjustment the best source of information about doing that would be your state universities Cooperative Extension Service. They will be able to tell you what your soils pH is, after a soil test, and what and how much material is needed to lower that pH. As a general rule of thumb it takes about 1 pound of sulfur per one hundred squaer feet of garden to lower the ph 1 point.