To configure the Cisco ASA via ASDM for SNMPv3, the administrator needs to perform two main tasks: specify an SNMP user group and add an SNMP USM entry. An SNMP user group defines the access level and security model for a group of SNMP users. An SNMP USM entry defines the authentication and encryption parameters for a specific SNMP user. These two tasks are required for SNMPv3 because it uses a user-based security model (USM) that provides secure access to the MIB objects. SNMPv3 does not use a community string, which is a shared password used by SNMPv1 and SNMPv2c. The SNMP manager and UDP port are optional parameters that can be specified to customize the SNMP communication. The SNMP host access entry is also optional and can be used to restrict the access of SNMP hosts to specific interfaces or networks. References :=

Some possible references are:

SNMP Configuration, Verification and Troubleshooting on ASA

How to configure SNMP v3 on Cisco Switch, Router, ASA, Nexus

SNMP Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3850 Switches)