I don't know if this is the best way to do it but it's definitely a way
NSMutableAttributedString *attributeString = [[NSMutableAttributedString alloc] initWithString:cell.textLabel.text];
[attributeString addAttribute:NSStrikethroughStyleAttributeName
value:@2
range:NSMakeRange(0, [attributeString length])];
[attributeString addAttribute:NSStrikethroughColorAttributeName value:[UIColor redColor] range:NSMakeRange(0, [attributeString length])];
cell.textLabel.attributedText = attributeString;
You can change the color of the strikethrough as you please.