Many people said that taking off the screen for the first time was a bit harder, maybe this link can be of help:
Don’t worry, the phone was built to be taken apart, that’s why you don’t even need tools for getting off the screen. However, since it also is the very first modular phone on the market, it may have some rough edges, which is, that some people reported some problems could be fixed by reassembling certain parts. It might be the downside of this revolutionary design, that in some cases contacts could get lose.
Anyhow, I hope you can solve your problem by resetting the battery already. Good luck!