Best free marketing courses/guides for bootstrapped startups?

Running a small SaaS and our marketing budget is basically zero.

I've tried following free marketing advice online but it's either outdated SEO tactics or stuff that tells you to just run Facebook ads.

Looking for free marketing courses/guides that teach practical strategies for getting customers without paid ads. We're willing to put in work but need actual direction on what to do.

Has anyone found free resources that taught you something that actually worked?

Not looking for theory, need stuff I can implement this week and see if it moves the needle.