The auxiliary verb did is not conjugated. It is the same for all persons (I did, you did, he did etc). And the base form and past form do not change. Look at these examples with the main verbs go and work:
Business International helps people to start and grow their own business and create employment. We are a global network of independent with profit.
Irregular verbs are words that don't follow a predictable pattern, like adding -ed to form the past tense. Unfortunately, for people who like to follow rules closely, there are many irregular verbs in the English language. The only way to learn the conjugation of these verbs into tenses is to memorize them.