Hello @Anonymous
We do not need Teams Premium licensing in order to use DocuSign app within Microsoft Teams. Attached is the screenshot of my demo account and I have DocuSign app even when I am not licensed for Teams Premium SKU.
I would advise check with your IT administrator as it is possible that DocuSign app might be disabled within your tenant. Otherwise I do not see any other reason of DocuSign not being accessed. Although there is one thing to note as this app is third party - you need to sign up for DocuSign in order to use it with Microsoft Teams.
Please let me know if it answers your query.