Hi, since the DKIM is a technical signature added to the email to certify the sender and a DKIM record should be added to the DNS to verify that signature, it could be that you have in place the DKIM at all. The signature is usually applied by the service delivering the email (not the plugin that uses the service to send it).
The DMARC is a set of rules used by who receive email from your address and they state how to deal with those email. For example,the DMARC default states the receiver should “quarantine” email from your address that does not pass the DKIM check or the SPF check.
I don’t think there is a way to set the dmarc to ignore the dkim check, it can only be set to “relaxed”. Then it is the receiver that decides how to deal with the email, maybe using other signals.
Ask the provider if they support the dkim signature and they’ll give you the dkim record to add to the DNS (that is the standard procedure when using a delivery service like Amazon, SMTP2Go, Sendgrid and so on).