You want to build a second PRI on your DIU2U, and add it to Trunk Group 2. The original trunk resides at PEN 1-23-1-0. I assume the new trunk will reside at 1-23-1-1 (the second port on shelf 23, slot 1's DIU2U).
Your trunk group 2 is currently limited to 24 channels. So first, perform CHA-BUEND for trunk group 2, and change the number of channels to 46 (23 channels per PRI).
Then REGEN the trunk circuit 1-23-1-0. Using your ComWin skills, transfer the REGEN'ed AMO TDCSU to the ComWin/Expert Access "buffer" (where you type in ComWin), and change the PEN from 1-23-1-0 to 1-23-1-1. I am assuming that you are using the same credentials for this second circuit as you used for the first circuit e.g. COS. Your current 1-23-1-0 circuit has two parameters that help identify the circuit at the TELCO. These two parameters are currently set to IGN=23 and IID=1. Change these to the numbers provided by the TELCO. If the TELCO did not provide you with these numbers, then you must change the parameters regardless. You are not allowed to re-use the same two numbers. Press the enter key, and see what happens. The circuit should be added successfully unless you have a capacity problem in DIMSU.
Caution: You are adding a second PRI to IP shelf 23. The NCUI resides in the center slot of your shelf. There are 128 timeslots on either side of this NCUI. If the slots to the left of your NCUI are heavily populated with station boards e.g. SLMO, SLMA, or gateway boards e.g. STMI, then you may have created "blockage" by adding that second PRI. The 4K is a TDM switch, meaning that every telephony action begins with a TIMESLOT. If everyone/everything to the LEFT of shelf 23's NCUI goes off-hook, will everything be assigned a timeslot? The two PRIs now need 46 timeslots to function properly, which leaves you with 82 available timeslots on the LEFT side of that shelf. Are there more than 82 stations and/or trunks residing there? If so, this timeslot "blockage" could possibly cause problems during high traffic periods. As with any TDM switch - everything should be OK unless there's a need for everyone to use the phones simultaneously.
You can check the status of the new PRI circuit by using this command: DIS-SDSU:ALL,,PEN,PER3,1,23,1,1; All channels should indicate "READY".
Good luck.