@TechUser2020-6505 Thank you for reaching out to us.
As I understand you are looking for an option to update the certificate ( new ) from automatically to ServiceNow.
Did a quick repro at my end, I see there is App Federation Metadata Url ( available under SAML Signing Certificate Section ) which has certificate information which can be consumed by the application. this contains Active/Inactive certificate information.
Let me know if you have any further questions.