> Is it possible to tune this type of concertina and if so how?

The short answers would be "Yes" and "Carefully".

Any free reed can be taken up in pitch by filing it a tad thinner near the free end, or down by filing it a millitad thinner near the fixed end. But it's very easy to go too far and wreck the reed. If one of my concertinas needs tuning I take it to an expert.