How do I Know if my piano can be tuned

First, you can test with a standard tuner, or download a tuning app on your smartphone. Try the center notes to see how far from standard tuning they are. If a note is more than a whole note (two steps) flat, it’s possible (but not necessarily immpossible) that the strings are too far gone to be brought up to standard 440 tuning. If a middle C note is at B flat or lower, the less likely it is that it can be brought up to pitch. It may still be possible to tune the piano to itself and sound somewhat playable.