This works great for me.
Create a new thread group at the bottom of the test plan and place a simple controller in it. Inside the simple controller, enter the code you want to repeat. I use two simple controllers, but one of them is actually a set of test tests for the database. Keeping all the threads included in the group, make sure that the thread group itself is disabled, otherwise it will run again by itself.
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Simple Controller Simple Controller, db.
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