How to remove attributes from the NSAttributedString swift?

It is very simple. You can use this method from NSMutableAttributedString class

func removeAttribute(_ name: String,
               range range: NSRange)

In your case

attr.removeAttribute(NSStrikethroughStyleAttributeName , range:NSMakeRange(0, attr.length))

Use the removeAttribute method:

attr.removeAttribute(NSStrikethroughStyleAttributeName, range: NSMakeRange(0, attr.length))

In Swift 5

let attributeString: NSMutableAttributedString =  NSMutableAttributedString(string: "YourStringHere")
attributeString.removeAttribute(NSAttributedString.Key.strikethroughStyle, range: NSMakeRange(0, attributeString.length))
yourLblHere.attributedText = attributeString