Tune hubs utilize shims to adjust preload and take up any free play in the hub. They come pre-adjusted from the factory when new with a few shims installed to account for differences in manufacturing tolerances. Some adjustments may be needed over time as the bearings wear with normal use and the bearing clearance increases.
This page on the Tune website shows the adjustment process for the front hubs: Assembly- & disassembly hubs - tune Helpdesk - Manuals, warranty information, and more. It’s a really easy process to remove the end cap to add/remove shims.
Tune offers a shim set comprised of 17mm ID x 24mm OD shims of 0.1, 0.15, and 0.2mm thickness. Unfortunately, this is not something that you can purchase directly from Tune as a consumer, and we do not carry this part on hand. Fairwheel Bikes is a US importer/distributor of Tune products and may carry, or be able to order, the shim sets.