Why my iPhone 7 shows no modem firmware and battery only show 1%

It’s hard to say exactly what the issue is but it obviously has to do with your Tristar replacement attempt. The first thing to do is to inspect your work. Look for bridged or dislodged components near Tristar and the surrounding area. You may want to consider reballing/replacing Tristar again. If you are inexperienced, then it is probably an issue with your technique. If you are experienced, then you should be able to tell of the placement looks good or not. For the SWI line, open up the schematic and follow the netline and inspect all of the components on that line.

As for the Modem firmware issue, this is most likely collateral damage. Again, check for bridging/dislodged components. However, focus on your Tristar issue first.