Once you login to your Pepipost account, go to Settings --> Sending Domain.
There you will see the list of Sending Domains. Click on "View Settings" link and by default, you will see the SPF and DKIM settings which need to be updated on your domain's DNS.
In case you have added a sub-domain then, you need to select the Preferred mode of verification as
SPF/DKIM.
You can refer this document for details:
https://docs.pepipost.com/docs/use-dns-to-validate-domain-ownership
Hope this information helped.