ChirpStack update on rPi4 w RAK2287

Can I update ChirpStack on my Gateway (RAK2287 on rPi4) without reinstalling the entire RAK bundled firmware and reconfiguring the rPi from scratch?

I get an error message when I run sudo apt update:

Err:5 Index of /packages/3.x/deb/ stable Release
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate. Could not handshake: Error in the certificate verification. [IP: xxx]
Reading package lists… Done
E: The repository ‘Index of /packages/3.x/deb/ stable Release’ no longer has a Release file.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.