Hi,
First of all ADFS is a SAML identity provider. Please check this page which is telling you how to export the SAML metadata of your UAG and import it in to your ADFS server. In this XML file the certificate is included.
https://my-virt.alfadir.net/index.php/2022/02/16/adfs-with-vmware-unified-access-gateway-uag/
Do not override or delete your existing relaying party! Always check your claims (User-principal-name to NameID). When the new relaying party is working, you can disable the other one. After a few days without any issue you can consider to delete it.
Please note that you don’t have to download the Metadata file of your ADFS server. No changes needed to your UAG configuration this time (at least until your adfs token signing certificate is replaced).
If you need some more assistance, please let me know.