I have a GitHub merging conflict and the conflict is showing that I have a teammates work included in mine yet I don’t

Question

I’m currently doing a project with a team of four on GitHub, so one teammate of mine created a feature branch and published it and it had code similar to what I wanted to do in my feature so I created a feature branch off his and went on to make necessary adjustments to it and published mine as well. Well when I merge to the development branch where we merge all our features, I get a conflict showing files that were on the initial branch that I used to create mine. What should I do?