I have understood the mechanism for converting ion 1 (benzyl alcohol) to ion 2 (m/z = 107) but not the mechanism for the conversion of ion 2 to ion 3 (m/z = 79). Please elaborate the mechanism for the conversion of ion 2 -> ion 3.
This is similar to the phenol fragmentation. In mass spectrometry, benzyl alcohol fragments with two mechanisms, the one in your question and by a simple loss of the OH(91m/z). The 79m/z is the fragment with the most intense peak.
I have added below two possible mechanisms for step 2 to 3.
EDIT: in the second option, the homolytic cleavage step is meant to be a summary of these steps:
The cycloheptatriene - norcaradiene tautomerization is a common equilibium. Usually the norcaradiene is present in small amounts, but as long as some is present the reaction can rapidly proceed through this intermediate.
In the diagram below, the norcaradiene can undergo hydrogen shift with concomitant decarbonylation to produce the m/z = 79 peak in the mass spectrum.