We present 0.075 (~400 pc) resolution ALMA observations of the [CII] and dustcontinuum emission from the host galaxy of the z=6.5406 quasar, P036+03. Wefind that the emission arises from a thin, rotating disk with an effectiveradius of 0.21" (1.1 kpc). The velocity dispersion of the disk is consistentwith a constant value of 66.4+-1.0 km/s, yielding a scale height of 80+-30 pc.The [CII] velocity field reveals a distortion that we attribute to a warp inthe disk. Modeling this warped disk yields an inclination estimate of 40.4+-1.3degrees and a rotational velocity of 116+-3 km/s. The resulting dynamical massestimate of (1.96+-0.10) x 10^10 Msun is lower than previous estimates, whichstrengthens the conclusion that the host galaxy is less massive than expectedbased on local scaling relations between the black hole mass and the hostgalaxy mass. Using archival MUSE Ly-alpha observations, we argue thatcounter-rotating halo gas could provide the torque needed to warp the disk. Wefurther detect a region with excess (15-sigma) dust continuum emission, whichis located 1.3 kpc northwest of the galaxy's center and is gravitationallyunstable (Toomre-Q < 0.04). We posit this is a star-forming region whoseformation was triggered by the warp, because the region is located within apart of the warped disk where gas can efficiently lose angular momentum. Thecombined ALMA and MUSE imaging provides a unique view of how gas interactionswithin the disk-halo interface can influence the growth of massive galaxieswithin the first billion years of the universe.