For 32-bit, the aql32.xla file is best placed in:

Program Files (x86)\Microsoft Office\root\Office16\Library

For 64-bit, the aql64.xla file is best placed in:

Program Files\Microsoft Office\root\Office16\Library

Once installed, it is necessary to set up the location in Excel: navigate to File>Options>Add-ins, select Aql32/64 in the table and then select Go. If a spreadsheet that already has calls to AQL in it is copied from another computer, the spreadsheet may not run properly on the new computer if AQL is installed in different directories on the two machines.