I wanted to know that
(1) Knowingly or unknowingly if we eat finger fish made from haram fish then what is the punishment of this?
(2) If there any way to purify ourself after we realize we have eaten haram food?
(3) The salat of that person will be accepted or not?

1- If one ate it unknowingly them it’s ok. If one did so knowingly then one must repent
2- You can fast for a few days and lose some weight. It would help in purifying the body. Also increase doing good deeds, as they compensate for sins committed
3- The salat is technically valid, but if one eats haram and doesn’t repent, Allah may not give much reward for this salat