Setting up mTLS for one broker identity provider


I have a realm with some identity-brokering already configured mostly with SAML, and I need to integrate a new IdP broker but with mTLS authentication.
The provider sent me the certificates but I don’t know how to set it up into my broker configuration to be able to have mTLS working between my keycloak server and their IdP server.
All the other providers didn’t ask me such thing,

Could you pls help me with this ?
Best regards,