Seguir is a stem-changing verb, so to form its present subjunctive we need its irregular stem sig-. Notice that the u from the infinitive disappears!

What is seguir yo form?

The imperfect root of Seguir is seguía. The imperfect tense is rarely irregular and can be easily conjugated from this form, which is the yo, and él/ella conjugation.

Why is seguir irregular?

What makes seguir an irregular verb is that it doesn’t follow the traditional rules for Spanish verbs ending in ir, er, or ar. In regular verbs, the stem of the verb doesn’t change no matter how you conjugate it. For example, amar (to love) is a regular verb.