Krsna gives him the power to see anything he wants to see, past, present and future. Thus by the mercy of Krsna, Arjuna is able to see everything. BG 1972 purports

Expressions researched:
"Kṛṣṇa gives him the power to see anything he wants to see, past, present and future. Thus by the mercy of Kṛṣṇa, Arjuna is able to see everything"

Bhagavad-gita As it is

BG Chapters 7 - 12

No one can see the entire universe sitting in one place. Even the most advanced scientist cannot see what is going on in other parts of the universe. Kṛṣṇa gives him the power to see anything he wants to see, past, present and future. Thus by the mercy of Kṛṣṇa, Arjuna is able to see everything.

BG 11.7 (1972), Translation and Purport

Whatever you wish to see can be seen all at once in this body. This universal form can show you all that you now desire, as well as whatever you may desire in the future. Everything is here completely.

No one can see the entire universe sitting in one place. Even the most advanced scientist cannot see what is going on in other parts of the universe. Kṛṣṇa gives him the power to see anything he wants to see, past, present and future. Thus by the mercy of Kṛṣṇa, Arjuna is able to see everything.