There’s no way to activate telecoil that I know of outside of the program options. And, just so you’re aware, there are actually two, telecoil programs. One, called, “T,” focuses exclusively on the telecoil stream, turning off your external microphones. the other, “MT,” focuses on the telecoil stream while also allowing you to hear other sounds through your mics (like if a partner or friend were sitting next to you and wanted to say something about the sermon, etc.). I think MT is the way to go, if you only have one program slot left to fill. If you have more, you could try both.
Within MT, your provider can then select the balance of sound (more telecoil/less environmental sound or the other way around), so you may need to experiment a bit. The app on your phone will also enable you to change the volume level of the telecoil or to mute the mics as options that are available to you in real time.