Absolutely you can start to DIY SEO your online profile. If you have the resource, knowledge and skill set to do so, you should.
There are some things to consider though when deciding to DIY SEO or not DIY SEO.
To get your website to page one in search engine results pages for competitive keywords and search terms, it takes a specific skill set as well as a lot of hours to do. You have to craft your own optimised content, create visual content and media, understand and be able to update your website including some technical updates, engage with other website owners and mangers to get backlinks … just to name a few things. This can take hours of your time which you may not have.
Search engines are constantly updating their algorithms too. Google makes minor changes to theirs multiple times a day with major changes announed and made less frequently. Staying up to date and being able to test what works and what doesn’t as well as analyse data and mine for usable insights, is all critical to your success.
Using an SEO agency just means you can focus on what you do best letting your SEO provider get you results faster.