So the conjugation of estudiar is
yo estudio
tú estudias
él/ella estudia
nosotros estudiamos
vosotros estudiáis
ellos/ellas estudian
Now to make a verb agree with the pronoun (yo, tú, él, ella, nosotros, vosotros, ellos, ellas) you must use the correct conjugation of the verb.
The conjugation of the verb estudiar that agrees with yo is estudio.
so your sentence would be:
Sí, yo estudio español en la escuela.
that translates to: Yes, I study spanish in the school.
if you want to say Yes, I study spanish in my school I would say
Sí, yo estudio español en mi escuela.
I hope this helps!