The Auto-Complete cache will fill itself automatically as it is based on people you've emailed before.
There has been a recent change (since Version 2110) which makes Outlook use the Global Address List as well for suggestions, whether you've emailed them before or not. That feature will become available in the Semi-Annual Channel in July.
If you still want to go the route of migrating the Auto-Complete cache or filling it with addresses see;
Backing up and restoring the AutoComplete cache of Outlook 2010, 2013, 2016, 2019 and Office 365
and;
Filling the Auto-Complete list with Contact addresses
For additional information, also see; AutoComplete not working as expected in Outlook