If you sent coins from D'CENT Wallet to an exchange without a Destination Tag (XRP) or Memo (XLM), you need to contact the exchange.
Check if the transaction is complete in the D'CENT App under "Details History". If completed, contact the exchange with your TXID (transaction hash) and D'CENT Wallet address.
❓ Related questions: How do I check if the transaction is complete?
❓ Related questions: What is a Destination Tag or Memo?