tips for moving from legacy system to more agile approach

our team is a small team consisting of only 6 people on software side including me. One handle android app, one iOS, one frontend, me and one another guy handles backend. i am still new and don't understand backend code fully.

Now we want to move on from legacy system especially backend to a more modern agile approach with xp and other things like ci/cd.

I am still new to all these concepts and only knows theory of them. i still have to see how things work practically.

So, Any tips for a beginner and how to setup a company culture(idk, if this is the word i am looking for)…