How can I reverse proxy and appliance that is using a self signed cert

[genfoch01]

I have an old readynas box. It forces https upon connection and uses its own self signed cert. To stop all the browser errors I get when I connect I thought I'd use nginx reverse proxy. No dice

"x.y.z uses an invalid security certificate the certificate is not trusted because it is self signed "

note1: x.y.z is the name used on proxy manager for this device
the cert here is not self signed as I got it from lets encrypt
note2: the readynas does have a self signed cert

note3: yes I might be able to hack the readynas to turn off ssl (which I think would fix my issue ) but the next update would put be right back where I started so I'm lookin for a more permanent approach.

note4: I do not have a lot of experience with this kind of problem so I'm not sure the correct questions to ask. I can't be the only one with this issue, there must be a solution. I read about using squid to remove the ssl but am not sure how to implement that and then pass the traffic to proxy manager.

I will provide any information that might be helpful. I would really apricate any info or links that would point me in the right direction.