Apple has several helpful tips for Vision Pro users who are not getting a comfortable and tight fit.
Fit is an important aspect when using the Vision Pro as it could lead to discomfort and a blurry display if not done right. To counteract these issues, Apple has published support documents to handle eye setup and light leakage concerns, as well as how to get a good headset fit.

To start, Apple introduced the Dual Loop Band and Solo Knit Band, and recommended that users pick the one that’s most comfortable for them and go from there. The support document further provides tips on adjustment, such as rotating the Fit Dial to tighten or loosen it, lowering or raising the band to fix pressure for the Solo Knit, while changing strap lengths to relieve pressure in various areas. Realigning displays and fixing light leakage are also part of the support document.