The functionality can be configured in Software configuration → Permissions → Autoassign records
The following settings blocks are available in the panel:
In the first section of the settings there are three places where automatic assignment process can be started.
Selecting this option will make it available in workflow actions, which will enable e.g. automatic assignment of already existing entries.
The option activates automatic record assignment only for newly created records, i.e. before their creation.
This option allows you to manually assign a record. If all the conditions are met, i.e. the criteria set for the record and the permission to the automatic assignment action has been granted in the profile of a given user, the manual assignment button will appear on the record preview.
Once you click the button you will see a popup with properly sorted users who can be assigned to the records.