How is HMAC hashed message decrypted on the receiver side We know that MAC algorithm and key are used in both sender and receiver side to get the matching MAC tages to prove that the data is authentic.

Now in HMAC we know that, it makes use of crytographic hash function which is irreversible, so when we use HMAC from the sender side to encypt a message using the HMAC formula, then at the sender side how will the receiver decrypt the message (hash function is irreversible), so how is the message at the receiver end, integrity is preserved and validated? Please explain.
Actually the HMAC value is not decrypted at all. The recipient takes all the needed input and she computes the HMAC on her own side and check if the result she got it is equal to the value on the message she got. 

You can roughly see the HMAC algorithm as an symmetric key signature. You cannot decrypt an HMAC, you only check that the value is correct.