Dial Phone number + Extension Number

[streetboy]

VERSION: 2.14-859a, BUILD: 220623-0824, Dedicated Server

So, we have data in the below format. The phone number and Extension number to be dialed is predefined in the data, And we want to dial the number first, once the call is connected into IVR then we want to dial the specific extension. All through auto dialing, not manual dial. How can we achieve that? Any suggestions

Number Ext CustName
999-999-9999 568 ABC
999-999-9999 458 DEF
999-999-9999 963 GHI

Thanks in advance.