Albert Barnes Commentary Jeremiah 44:3

"because of their wickedness which they have committed to provoke me to anger, in that they went to burn incense, [and] to serve other gods, that they knew not, neither they, nor ye, nor your fathers." — Jeremiah 44:3 (ASV)

In that they went to burn incense, and to serve - Or, by going to burn incense to serve other gods by that means.