How do you fix missing dll files on Windows 11?

A couple of years ago I purchased and downloaded some software from NIST in USA called REFPROP.  This is an industry standard used by chemical engineers and by other software for substance properties prediction.
I wanted to use the software via a dll call from Excel.  The software was written as 32 bit and the installation software therefore put it in the Program Files (x86) folder.  The only way around this - so far - was to copy over the relevant DLL files into the Program Files folder.
When starting Excel it automatically looks in the x86 folder and so I go to Options>Add-ins>Go> then Browse (as Roaming sends it to the X86 folder) to Windows(C:)>Program files>REFPROP> and click the Excel Add-in. and click OK. 

I get a message that it cannot find the ...xla it in the x86 folder - which I ignore and accept deletion from the list.
I can then open my Excel files (of which I have a lot) and the links to REFPROP work just fine.
This is a slightly tedious solution, but it works OK.
If there is a more elegant approach I would be interested to try.