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.
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.)