BG 18.62 reads as
tam eva śaraṇaṁ gaccha sarva-bhāvena bhārata
O scion of Bharata, surrender unto Him utterly.
iti te jñānam ākhyātaṁ guhyād guhyataraṁ mayā
Thus I have explained to you knowledge still more conﬁdential
sarva-guhyatamaṁ bhūyaḥ śṛṇu me paramaṁ vacaḥ iṣṭo 'si me dṛḍham iti tato vakṣyāmi te hitam
Because you are My very dear friend, I am speaking to you My supreme instruction, the most conﬁdential knowledge of all. Hear this from Me, for it is for your beneﬁt.
sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja ahaṁ tvāṁ sarva-pāpebhyo mokṣayiṣyāmi mā śucaḥ
Abandon all varieties of religion and just surrender unto Me. I shall deliver you from all sinful reactions. Do not fear.
Krishna suggests to surrender in 18.62, and then calls it more confidential knowledge in 18.63. In 18.64,Krishna says he is going to teach most confidential knowledge and says in 18.66 to surrender.
In 18.61-62 & 18.65-66, the process suggested is the same 'bhakti' /'surrender' . Then what is the most confidential thing that Krishna says in 18.64?