In Odoo the database id is auto generated and that field name in Odoo is "id". If you want to have previous system id in odoo you can use another field to store that value for you.
For this you can also use Odoo Studio App to create a custom code field on Contacts form and store that Id Value in this field when importing. And whenever you create a new contact add code field by yourself depending on sequence.

However, the default id field in Odoo is not controllable, that will be generated automatically when importing or creating records.

Hi everyone,

I’m trying to import my old customer ID numbers from Microsoft Nav into a CSV file, but every time I do, the system automatically generates a random number instead. Is there a way to prevent this? Can I just use the original customer IDs I had before?

Any advice would be appreciated!