I performed few transaction with minimum amount but the status of those transactions in History tab are Failed, are my coins lost?? How can get my asset back?

The required minimum amount on the wallet is only estimation. It may change when submitting on the blockchain, sometimes it is bigger than the time when the user submit "exchange" button. Thus, in this case, the transaction will be failed and Changelly will refund coins to you. It takes time to refund, so if you would like to check the status of refund process, please contact Changelly here