You can remove a promotion from your newsletter one of two ways. The first way is to go to Content→ Promotions and toggle off the promotion altogether. The second way is to change the start and end dates for the promotion. For example, if you just want your promotion to run for the month of October. The start date should be October 1, 2019 and the end date should be October 31, 2019. The promotion will not run outside those dates.