Query cannot open a Report.
You must have code or Macro somewhere in the process that execute an
OpenReport macro action (Macros) or method (VBA). If you can find the VBA
OpenReport statement, you can simply add 2 lines of code:
DoEvents
DoCmd.RunCommand acCmdZoom75
after the OpenReport statement.
You can change the Zoom factor when you preview the Report but it won't
stick, AFAIK. Next time you open the Report, Access will revert back to
whatever Access thinks suitable.