The first thing to do is eliminate all traces of the offending food from your diet. In the short term, this will make you feel better. In the long term, it May allow your body to “forget” about the allergy.
IGg cells are often responsible for delayed reaction allergies – where symptoms do not appear for hours or days. New IGg cells do not learn what to react to from old IGg cells, unless you are exposed to the allergen.
IGg cells are considered to have a half-life of about six weeks. As time passes, fewer and fewer of the old IGg cells that react to a particular food will be active in your body.
When all of the old IGg cells are gone (after about six months), the new ones should not react to the previously allergenic food. It is theoretically safe to eat the food again.
Note that this only applies to delayed-reaction allergies. This is not known to work for allergies where you get an immediate reaction to the food.
Also note that this does not always work. I have left some of my less serious allergies behind, but my wheat allergy continues to plague me.
The only way to find out if it works is to try it. You may want to eliminate the food for a year to be absolutely certain you have given this method the best chance of success.