Access management is closely related to which other process?

Capacity management is concerned with ensuring sufficient IT resources exist to meet current and future business demands, not with controlling who may use a service.

3rd line support is a support escalation tier for resolving complex technical incidents, not a process related to governing or enforcing access rights.

Access management is defined in ITIL as the process that grants authorized users the right to use a service while preventing access to non-authorized users, making it the operational implementation of information security management. Information security management sets the policies governing confidentiality, integrity, and availability, and access management enforces those policies on a day-to-day basis. The two processes are explicitly linked in the ITIL Service Operation and Service Design publications.

Change management controls the lifecycle of changes to IT services and infrastructure, which is a separate concern from granting or revoking user access privileges.