Is there any way to find out which unit of the US army of occupation took control of US HQ in Munich after April 30th, 1945?
It would be better to add more details, mainly what you understand as 'US HQ in Munich'.
The source below gives some details about the establishment of the Office of Military Government for Bavaria (OMGBY), which took place between the 14th of May and the 14th of June 1945.
It doesn't give any exact details as to where in Munich they were stationed, but there are details with names, dates and units which may be of help.
Immediately after the occupation, the Military Gouvernment Detachment E1F3, headed by Colonel Charles E. Keegan, took over the administration of the occupied country on May 14, 1945. Initially, the detachment was limited to the part of Bavaria that had been occupied by the 7th Army. In addition, there were other types of detachment that had different territorial responsibilities. Ebersberg, for example, belonged to type D, which was responsible for the urban and rural districts (DET I1F2, then I-361).
Establishment of the American military government in Bavaria (OMGBY)
After the 3rd Army had been assigned Bavaria as the final occupation area (Eastern Military District) on June 14, 1945, the command overriding the detachments, the G-5 staff division of the 3rd Army, moved its headquarters from Erlangen to Munich. This G-5 Section was in turn subordinate to the G-5 Division USFET (US Forces European Theater), the division of the American General Staff responsible for military government under General Dwight D. Eisenhower. In parallel, the US Group Control Council (USGCC) worked under General Lucius D. Clay, which represented the USA at the Allied Control Council, which met for the first time on July 30, 1945. The task of the USGCC was to implement the decisions of the Control Council in the occupied area, although this could only be done via the G-5 division USFET. As this was a cumbersome process, the USGCC was transformed into the Office of Military Government US (OMGUS) as part of the spin-off of the military government from the general military command structure. At the same time, the three states of Greater Hesse, Württemberg-Baden and Bavaria came into being in the American occupation zone with Proclamation No. 2 of September 19, 1945, each of which has had its own regional Offices of Military Government under the direction of a Land Director since October 1, 1945 goods: in Bavaria the Office of Military Government for Bavaria (OMGBY).
- Einführung OMGB - Military Gouvernment (in German)