Attached is a screenshot of Toolset > Post Forms
As you see it cannot be that the ScreenShot you share depicts Toolset Forms autogenerated in the thousands.
There is no such feature that could do that (Automatically generate Forms).
The ScreenShot you show is probably from Dashboard > Pages or Dashboard > Any Post Type, and there you have thousands of posts, that you did not add your self.
Is this correct?
Toolset Forms cannot add posts itself automatically either.
Someone needs to submit the Form to create a Post.
Given the titles of those posts it seems to me (also considering you mention an import) that you imported the Toolset Forms several times to Pages Post Type.
This is however not due to Toolset, it may be due to the import process.
There are no users reporting this issue, that I can find.
Can you link me to some?
It would be crucial to solve such bug fast.
For now, I suspect the import with (any) tool you used to migrate the site or import content generated those posts.
To delete them you can either display 100 posts a time in that list and click 20 times on delete, this should remove the posts in less than 20 minutes.
It's tedious though, and if you prefer, and know what posts you want to delete, we could do that in the database.
It's however safer, and faster, in the WordPress Admin.
Just list 100 (or more, depends on your server) posts a time, then check them all and move to trash, repeat in the trash to delete completely.
This is an OK workaround if this is a unique situation.
If not, if those posts keep coming, we need to know why this happens.
Since Forms cannot do that without explicit submit, we would need to know if it happens without any other plugin but Toolset and a Native WordPress theme as well.
If then the issue persist, we will need precise steps to either replicate this on a fresh install or on a copy of your site.
Please let me know the outcome, so we can then decide how to proceed.