You can configure Redis connection parameters using REDIS_URL Flask configuration variable with redis+sentinel URL scheme:
redis+sentinel://localhost:26379[,otherhost:26379,...]/mymaster/0
redis+sentinel://localhost:26379[,otherhost:26379,...]/mymaster/0?socket_timeout=0.1
redis+sentinel://localhost:26379[,otherhost:26379,...]/mymaster/0?sentinel_socket_timeout=0.1
redis+sentinel://:sentinel-secret-password@localhost:26379[,otherhost:26379,...]/mymaster/0?sentinel_socket_timeout=0.1