They can steer the balloons using altitude and upper level air currents. Google has a bunch of their Loon balloons that can be tracked on any ADS flight tracking software. I think the last balloon was at 60k in altitude.
Loon deployed its high-altitude balloon network into the stratosphere, between altitudes of 18 km and 25 km. The company stated that the particular altitude and layer of the stratosphere is advantageous for the balloons because of its low wind speeds, which are usually recorded between 5 mph and 20 mph (10 km/h to 30 km/h). The layer is also an area of minimal turbulence. The company said it was able to model the seasonal, longitudinal and latitudinal wind speed variations, allowing them to adjust the placements of their balloons.[38]
Loon claimed it could control the latitudinal and longitudinal position of its high-altitude balloons by changing their altitude. They did this by adjusting the volume and density of internal gas (which is composed of either helium, hydrogen or another lighter-than-air substance), which allowed the balloon's variable buoyancy system to control the altitude. Additionally, Google had indicated that the balloons were possibly constructed from materials like metalized Mylar, BoPET, or a highly flexible latex or rubber material, like chloroprene.[38]