HEADERS

I am not a regular user of WordPress, so please bear with me.
I set up my blog ipensionati.com in 2019. Used a plug in to create an image header unique to each post —Unique Headers (v1.8.1 by Ryan Hellyer). Worked great. Now, when I try, I am unable to add a header. I read Hellyer’s website that suggested I also install his plug in Unique Headers Single Posts (v1.5). Did not help.

The sidebar no longer shows the option for the headers.

I am using the theme “Sketch”

Thanks in advance for anyone’s help