How do i turn off screen overlay on my s7 edge

Every time I click on an app today it is bringing up a message that I need to turn off screen overlay first when I click on it it brings up a list of apps I have turned all of them to off but still had no joy all day i have had this problem I honestly don't know what to do to get my phone to work again and dont understand why this has started happening but I can't use the apps untill this has been turned off please can anyone help me sort this problem out many thanks to all in advance

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