You can follow these steps:

Step 1: In Odoo 14 and Odoo 16, create a field named Code in the model mail.channel. Then set the Code value for the mail.channel records in Odoo 14 so that these values are unique.

Step 2: In Odoo 14, export the mail.channel records including both Code and ID fields (note ID, not External ID).

Step 3: Import data from the mail.channel file exported above into Odoo 16.

Step 4: In Odoo 16, export the mail.channel records including both Code and ID fields (note ID, not External ID) to get the id.

Step 5: In Odoo 14, export mail.message data and use Excel's vlookup function to get the Code of mail.channel records. Using this Code vlook in the mail.channel file  exported from Odoo 16 will have the id of the corresponding mail.channel records in Odoo 16 to import.

Note: If the number of records is too much, you can consider using the following module to support import to avoid timeouts: https://apps.odoo.com/apps/modules/16.0/vks_import_excel.

Hi,

You can import chat details by enabling debug mode and going to Settings -> Technical -> Messages.

Hope it helps