Snipe-IT custom fields can be synced, displayed, and edited in the asset details view of your Jira issues.
Navigate to the Snipe-IT for Jira configuration page: Jira settings > Apps > Snipe-IT for Jira > Configuration
In the menu item Show custom fields in asset details select in the dropdown the custom fields that should be displayed
Select Allow editing Snipe-IT assets from Jira to enable editing assets within Jira. You can then select which fields can be edited via the dropdown Allow editing of fields.
Read more about which asset details can be edited from Jira.