The import is based on an export from OpenEMR backup export i.e. another or current instance.
Also note the export is generally a sql file. Similar as if you exported from phpMyadmin.
So from the screen for import you would need to browse to where the export file is and select for import. Maybe view the file for import to get an idea of what is being imported.
You can also use csv I believe but I’ve never used.
I strongly advise that you implement our current release v6.0.0(2) and since you’ve already installed v5.0.2 then try to get you LBF imported then upgrade your 5.0.2 to v6.
I also strongly advise backing up before importing LBFs in case …