To set sag on a dirt bike by yourself, follow these steps:
1. Identify the preload adjustment on the rear shock, usually a collar above the spring.
2. Tighten the adjustment to compress the spring and increase preload, raising the bike's resting position.
3. Loosen the adjustment to lower the bike.
4. Use a spanner or shock punch to spin the preload adjuster.
5. Tighten or loosen the shock collar to adjust the tension on the spring and achieve the desired sag.