I solved it
In env file
there was,
DB_HOST=mysql
DB_PORT=3306
DB_DATABASE=xxxxx
DB_USERNAME=xxxxx
DB_PASSWORD=xxxxx
and then added following lines.
DB_HOST1=172.xx.xx.xx ← ip of mysql container.
DB_PORT1=3306
DB_DATABASE1=xxxxx
DB_USERNAME1=xxxxx
DB_PASSWORD1=xxxxx
Inspired from
In issue #368 there is mentioned Code part line 39