You need to close the bleed air to the affected engine and pull out the checklist.
Everything here is from the references shown below, with a few comments in an alternate color.
L Start Vlv Fail Open
R Start Vlv Fail Open
L-R Start Vlv Fail Open
Gulfstream GVII-G500 Airplane Flight Manual, Revision 4, August 29, 2019
Gulfstream GVII-G500 Production Aircraft Systems, Revision 3, July 15, 2019
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