Strictly speaking, Luffy does not have any technique known as Gear 1. The techniques he has used so far range from Gear 2 to Gear 5 with no mention of Gear 1.
Monkey D. Luffy, popularly known as Straw Hat Luffy, is the captain of the infamous pirate crew, the Straw Hat Pirates, and the protagonist of the series. Luffy is a rather fun-loving and easy-going guy until something threatens the well-being of his loved ones, then he is a formidable unstoppable force.
Although he may not look like it based on his thin physique, Luffy is very strong. He once knocked out 50,000 fishmen in a battle in the Ryugu Kingdom with his Conqueror Haki (also known as the Color of the Supreme King) alone. That’s not all - he is also exceptional in hand-to-hand battles and fights at multiple stages. In his journey so far, Luffy has fought against many formidable opponents and even got beaten up from time to time. To protect his friends, he trained hard and grew stronger. With his training, he came up with several fighting forms, which he refers to as Gears. So far, Luffy has used 4 Gears, starting from Gear 2 to Gear 5.
As Luffy refers to his transformations as gears and the first gear introduced was gear 2, it does pose the question, does Luffy also have a Gear 1 fighting technique? Unfortunately, so far in the series, Luffy has not referred to any of his fighting techniques as Gear 1. But if we take Luffy’s simple nature and his other battle techniques into consideration, Gear 1 could be just his base form, his regular fighting style, and when he came up with a more powerful technique, he named it Gear 2, kind of like an upgrade to his previous fighting style.
Again, there is not a single mention that any of Luffy’s abilities are called Gear 1, so it does not exist so far. All we can do is assume that Gear 2 is an upgrade to his basic form, so chronologically his base form or his regular fighting style would be Gear 1. Unless any future updates or any information relevant to the matter comes to light, all we can say for sure for now is that Gear 1 does not exist so far.