As romullus said, if you just want to keep the Specular workflow then switch your Corona Physical Advanced Options to: Glossiness/Specular.
If you need an IOR conversion you can use Substance Designer for this. I wrote an article about this before Corona had Physical but the same concept will apply now. Search the article for "Specular Color & Specular Level".
https://jamesvella.net/2020/04/20/2019-9-2-substance-designer-to-vraycorona/If your textures are simple and all you want is a 1/IOR conversion for a non-metal then your IOR color should be: 0.666667 (linear color texture) for 1.5 Fresnel.
if your textures are simple and metal then its: .000992 (linear color texture). Or just use the metal option in Corona.
I have some formulas in the article you can run in python, a calculator or in Substance that do the conversion for other Fresnel values.
If you have mixed metal with non-metal then it gets more complex (for example chipped painted metal or some mixed unwrap). In that case you will need to separate the specular color out and place it back into your Diffuse texture accordingly and then do the IOR conversion.
In my opinion unless you really need the IOR texture I would just use the numerical values to control the Fresnel, since then all you need to think about is getting the specular color back into the Diffuse. Or just go with romullus suggestion.
