how do you get a cover line??

I'm new to charting so I have no idea really, but after years of not being able to fall pregnant I'm trying to track my temp to see if it helps 🙏 I notice all the charts have a cover line, how do I get mine to show? Or is there a reason why it's not showing? I have added both charts from glow and fertility friend as both don't have a cover line.
Thanks in advance do any tips and advice!