An air carrier First Officer reported the ILS was not loaded into the FMS properly resulting in an unstable approach below the glidepath and a low altitude alert from ATC.

Narrative

We were on the FMS Visual XXR into ZZZ. It was my leg and I had the ILS frequency dialed in but did not check the course prior to switching green needles and was planning to join the approach. I had dialed up the altitude preselect knob so it would continue a descent as I caught the glide slope. When I switched to green needles the course was not tuned correctly and it threw me off. I descended lower than intended; clicked the autopilot off to override and leveled at about 900 feet. ATC came on frequency close to the same time and said we had an altitude alert and to stop descending. We had stopped and I held altitude. My Captain was a little behind so I tuned my ILS course into the correct radial and resumed descending when the glide slope came in. We were unstable at less than 1;000 feet; further out than we should have been. I continued to landing after becoming stable again. Cause: We had been issued the FMS and while we had briefed it; I was still thinking about green needles but because the FMS didn't have the ILS loaded; the course wasn't tuned in. I asked the captain to tune my course correctly but he did not change it so I reached up and did it. Suggestion: It would have been better to capture in white needles and just followed the snowflake down. It was a pilot error because I didn't use my automation correctly; or the way I planned. We were unstable at a low altitude and in hindsight should have executed a go around just like we always brief. I think we were both in relaxed awareness and I should have spoken up and rejected the landing; even if everything turned out fine.