SPF
Add include:spf.titan.email to your existing SPF record. Do not create a second record: two SPF records mean neither works, and that is the most common mistake in this whole area.
A complete record with Titan alone looks like v=spf1 include:spf.titan.email ~all. If you use other sending tools, their includes go in the same record.
DKIM
Found in Titan control panel, under Settings, then Domain settings.
Titan is often resold through a registrar or hosting provider, so the DKIM records may already be published for you. Confirm rather than assume.
Titan publishes keys under the selector titan1 and titan2, which is what an external check looks for.
DMARC
DMARC is the same regardless of provider, because it is your instruction rather than theirs. Start at v=DMARC1; p=none; rua=mailto:you@yourdomain.com, read the reports for a few weeks, authorise everything legitimate, and only then tighten. The DMARC guide covers the order in detail, and the order is what stops you blocking your own invoices.
Worth knowing with Titan
Because Titan is usually sold as an add-on, the mailbox subscription and the domain renewal are separate charges on separate dates. Both need to be current.
Check it afterwards
Publishing the records is not the same as them working. Verify from outside: whether SPF passes, whether a DKIM signature is actually present, and how many lookups your SPF now performs. The free mail check answers all three in plain language.