Here are the steps to remove the add-in globally from all your users.
1️⃣ Go to Microsoft 365 Administration Center
2️⃣ Integrated Applications
On the left dropdown: View All > Settings > Integrated Applications
3️⃣ Click on the Signitic add-in in the list of apps
4️⃣ Remove app
Then check the validation box, and delete.
If you didn't manage to follow these steps, here is a gif to summarize the procedure.
