I have to replace our gone SEO expert but I'm a UX designer

I used to be a product designer (injection molding and 3D CAD design) but I've been learning UX&UI the last year's and I recently managed to land a job as a UX/UI designer for a startup here in Montreal, Canada.

The web platform I work for is a phone plan and home internet comparator that generates revenue through traffic resold to providers and also banner adds.

We have nearly 175k monthly users.

I have recently accepted the challenging task of SEO marketing (temporarily). I'm taking a Udemy course on that topic right now.

There is so much to learn that I'm not sure where to start. Can one of you SEO experts guide me on what they would do to improve our SEO ranking. I just need few bullet points and I'll do in dept research.

Thanks for your le help guys!

• I will put the url in the comments section in case one of you wants to have a look at it!