Well the backend DB part needs to be in a location that can be accessed internally or externally.
I do this via mapped drives and secure VPN.
So we have a corporate network drive (lets say X

shared from the main server file share (//servername/my_db_data) that would hold the backend DB.
The remote users fires up the VPN and establishes a secure connection to the corporate network. (ensure you set the users VPN client to use split tunnelling otherwise all the users internet traffic will go through your corporate network, not good!).
Then our user fires a simple batch script which maps the company network drives.
So the remote user now has a VPN connection to the corporate network and an identical X: drive, so when the front end opens and tries to talk to the backend DB on X:\my_db_data\my_backend_db.accdb , it is able to find the data and every thing works.
In my frontend app I actually use linked tables to SQL server using TCP/IP port 1433, but the principle is the same.
You may be able to use UNC paths instead so the linked data is via '//server/usershare' and then there is no need to do the mapped network drive.
I've not linked to another Access DB file for a long time so not sure if UNC is possible.
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