Since your first post 7 months has passed.
I was sure you have been able to exchange the Dash to the FIAT pair you wanted.
If not I repeat you must send the Dash you have in your wallet into the exchange in order to sell them and get the money on your bank account.
Also be sure you are using the updated wallet as 7 months ago we were using different wallet version (v 13.x) which is not good at the actual stage of the development, so you will have issues in syncing.
The actual version is v14.0.3 downloadable on dash.org website.
Let us know if you have more questions.
You mean you sent dash toward the dash wallet right?
Now you wnt to take them back to fiat (euro, dollar etc) right?
If so you must open the account on an eschange like kraken or uphold or bitfinex or whatever excahnge which support the fiat pairs.
Send coins ther after verified sell and withdraw to your bank account.