Both Rama and Hanuman were present on the chariot of Arjuna to help him. BG 1972 purports

Expressions researched:
"Now both Rāma and Hanumān were present on the chariot of Arjuna to help him"

Bhagavad-gita As it is

BG Chapters 1 - 6

The emblem of Hanumān on the flag of Arjuna is another sign of victory because Hanumān cooperated with Lord Rāma in the battle between Rāma and Rāvaṇa, and Lord Rāma emerged victorious. Now both Rāma and Hanumān were present on the chariot of Arjuna to help him.

BG 1.20 (1972), Translation and Purport

O King, at that time Arjuna, the son of Pāṇḍu, who was seated in his chariot, his flag marked with Hanumān, took up his bow and prepared to shoot his arrows, looking at the sons of Dhṛtarāṣṭra. O King, Arjuna then spoke to Hṛṣīkeśa [Kṛṣṇa] these words:

The battle was just about to begin. It is understood from the above statement that the sons of Dhṛtarāṣṭra were more or less disheartened by the unexpected arrangement of military force by the Pāṇḍavas, who were guided by the direct instructions of Lord Kṛṣṇa on the battlefield. The emblem of Hanumān on the flag of Arjuna is another sign of victory because Hanumān cooperated with Lord Rāma in the battle between Rāma and Rāvaṇa, and Lord Rāma emerged victorious. Now both Rāma and Hanumān were present on the chariot of Arjuna to help him. Lord Kṛṣṇa is Rāma Himself, and wherever Lord Rāma is, His eternal servitor Hanumān and His eternal consort Sītā, the goddess of fortune, are present. Therefore, Arjuna had no cause to fear any enemies whatsoever. And above all, the Lord of the senses, Lord Kṛṣṇa, was personally present to give him direction. Thus, all good counsel was available to Arjuna in the matter of executing the battle. In such auspicious conditions, arranged by the Lord for His eternal devotee, lay the signs of assured victory.