Once the outbreak clears, give it another 2 weeks before you reintroduce sweet potato again. Don't give me anything new except sweet potato. My lo was previously allergic to berries and tomatoes. I will feed it every 1.5months to see if he is still allergic to it (he gets itchy behind his knees and at his elbow). Eventually he stop itching at around 2 yrs old and he is eating lots of them now at 6 yrs old :)
Wow sweet potato allergy that's quite rare. You may want to try a little again after two months and if still allergic perhaps wait till after one year old. Babies can grow out of allergies. When he is older you may want to bring him to Kkh to do allergy test https://www.kkh.com.sg/Services/Children/AllergyService/Pages/Home.aspx
Yes try it again after a week. During this period do not give anything else except for the food you suspect. Other option is to go for a skin prick test. I did it for my son at KKH.
Offer it again (no other food) for 2 days in a row. If eczema returns on either of the days, don't offer sweet potato anymore.