Creating an Access team, from the UX perspective, is adding a subgrid (list of related records) to the form of table you want to distribute. This subgrid collects the users or teams who can get access (to view, edit or delete) to the given record (in addition to the user who is the owner of the record). It's just like "This is the list of users who can also get access to this record in addition to the owner of the record".
Access team is a team automatically generated for every record of the given type. Every record has its own, separate group of users who can view, edit, or delete this specific record + the owner of this record.
In your scenario, the user after the creation of the record needs to assign specific users or teams to the record by adding them to the record's access team. For example: I am a user from Germany but I created the record for Spain. I have to add the Spanish team to access the team of the record I just created. After that, I can get access to the record, because I am still the owner, and additionally all listed users in this record's access team have also access to the record.
If you want to do the process related only to the specific field on your form (I mean Country) you have to create a Power Automate Flow, which will be triggered after the creation of the record or changing its "Country" value. The Flow should remove all previously existing members of the Access team and add them to the specific Country Team dedicated to the given country.
