Changes to the Gerund
Spanish: Cambridge International GCSE, topic 10.3.2
Stems Ending in a Vowel
When the last letter of a verb stem is a vowel, the ER and IR gerund changes. Instead of 'iendo' it becomes 'yendo'. For example:

Ir → yendo

Oír → oyendo

Creer → creyendo

Construir → construyendo
Test yourself on Changes to the Gerund
What is the gerund of 'creer' in Spanish?
¿Cómo dirías 'going' en Español?