After you have added SIZE to your Gnosis Safe, you can submit an 30-min TWAP order just like the way you did on SIZE.
Type in the amount you'd like to swap, then hit "TWAP".
Hit "Confirm" after you've read everything about the trade.
Hit "Submit" on Gnosis Safe to submit your transaction.
Approve the transaction using Gnosis Safe
Approving transaction of SIZE bears no difference than approving a simple transfer using Gnosis Safe--you need to sign and execute it.
If you need to have more than one singature to approve the transaction, simply ask other multi-sig holders to sign and execute. They can find the pending transaction in the “Transaction“ tab in the left sidebar.