Complex sentence: On the 20th, he returned to Athletic Bilbao, qualifying for the Champions League in his first season and the Europa League in the second while also reaching the final of the 2015 Spanish Cup.
Split into simpler sentences: On the 20th, he returned to Athletic Bilbao,. In 2014-15, the team qualified for the Europa League while also reaching the final of the 2015 Spanish Cup.