Why do you wish to change the CA used here exactly?
The key presented is signed by a Certificate Authority: the internal Check Point one.
As it is used for a lot of things (including VPN), the internal CA cannot be removed.
You also cannot replace the internal CA with an external one.
I know for site-to-site VPNs for third parties, you can specify which Certificate Authorities can be used for VPN.
That's done here:
![Screen Shot 2020-04-05 at 8.40.52 PM.png Screen Shot 2020-04-05 at 8.40.52 PM.png](https://community.checkpoint.com/t5/image/serverpage/image-id/5394i17D96115962CE021/image-size/medium?v=v2&px=400)
To add a different trusted CA, you need to create an object for it:
![Screen Shot 2020-04-05 at 8.44.14 PM.png Screen Shot 2020-04-05 at 8.44.14 PM.png](https://community.checkpoint.com/t5/image/serverpage/image-id/5395i3F39133B52FA2FA1/image-size/medium?v=v2&px=400)
Whether that works for Remote Access VPN is a separate question.
Even if you could, I don't believe it changes the end user experience at all (i.e. they'll still get prompted to validate the site certificate when they first connect).