Access has a fatal flaw of a 2GB limit, which when combined with other problems means it's not usable.
MariaDB
Available from mariadb.org, choose the Windows 64 msi download.
Set up as service, use a root password, otherwise defaultss.
Download the java connector.
Importing into Access
The raw csv format tables can be imported as "Text File" (External Data tab).
Load PATIENT_ID as Short Text, since Long Integer is too short, and double has problems (at least 10 selected PATIENT_ID's would not match when used to select using the same ID).
Demographics
Import this as a table Patients. Let Access create a primary key and rename that to SubjectID.
Diagnoses
Set ENCOUNTER_ID to Short Text.
Encounters:
set PAT_ENC_CSN_ID to double
For Date, change name to DATE, and make sure it's month/day/year format ("Advanced" button at bottom-left.)