Could someone tell if we can convert an MP3 file to WAV format and regain the initial audio clarity? If so, how do I do that?
No. This is an information-theoretic impossibility.
MP3 is what is known as a "lossy" format, meaning that when you encode information into an MP3, some of it is lost (but, usually, not to the point that the listener can detect the loss in quality -- the goal of good lossy encoding is to lose information that the user couldn't detect anyway).
Once that information is "lost" by being encoded from a lossless source format into MP3, that information is permanently gone, unless you still have a copy of the source data. If all you have is the encoded MP3, it is permanently gone. There is absolutely NO way to get it back whatsoever.
You can convert your MP3 to a WAV or FLAC or other lossless format until the cows come home, but the original quality will not come back. If the source data is permanently gone, the only thing you could possibly do is attempt to "remaster" the waveform to increase its quality -- but even then, that is like painting over an existing painting... you are changing the essence of the work. You can't get back to the true, original data. It is gone, unless a copy of the lossless data exists somewhere.
Remastering is a very expensive process that involves a lot of manual labor and very advanced audio processing equipment. Big recording studios sometimes remaster old recordings to make their sound quality as good as (or nearly as good as) the sound quality of songs recorded in the studio today with modern audio equipment.
The basic elements of remastering involve a detailed knowledge of signal processing; as well as the ability to run a number of algorithms that find certain types of anomalies, or synthesize entirely new components to the sound. Remastering works best with music; it does not, typically, work very well with voice or other sound effects. Examples include:
The types of algorithms that can be applied to effectively remaster old analog recordings (from 40+ years ago) do not necessarily apply to restoring very low quality MP3s to a quality similar to the original audio. The reason is that the MP3 codec has somewhat unusual quality reductions that produce irregular and difficult-to-correct patterns in the waveform.