I made a recording of myself, standing upright, with a lapel mic. However, you hear the echo of the room too much. Is there a sound effect that makes my voice more "close-by" sounding?

Ones you have echo in the recording it’s almost impossible to remove it (no effect for echo removement in Kdenlive). Some hints: Move the mic closer to your mouth. Change into a smaller room. Change into a room with a lot of furniture and a “mess around” (no joke).