How to Manually Create External Account

We have multiple accounts we are unable to linked to Stessa and will manually import the data using CSV/OIF files, but we cannot separate imported data by account when the account cannot be linked. How can we “manually create external accounts” in Stessa so our imported data can be separated by account (instead of all of it in “Imported File”)?
FYI, we attempted to add a CSG Forte account using “Other Account”, but it cannot be linked, the account name does not appear as an option for the imported transaction. The Stessa message also states “Stessa does not support connecting to this Data Source yet. We are working on new integrations and will keep you updated.”