depends how you read an excel file, you can use python xlrd library or use it as if it as a normal table in ArcMap. Anyway just create a dictionary from your excel file,
myUpdatedCoordinates = {PNTID:(X,Y), ......PNTIDn:(Xn,Yn))
the loop thru your featureclass with an updateCursor,
with arcpy.da.UpdateCursor(fc, ['ID', 'SHAPE@']) as cur:
for row in cur:
if row[0] in myUpdatedCoordiantes:
newgeo = arcpy.PointGeometry(arcpy.Point(myUpdatedCoordinates[row[0]][0],myUpdatedCoordinates[row[0]][1]), spatialReference=XXXX)
row[1] = newgeo
cur.updateRow(row)