Unknown Number (2019)

They both have the element of two people communicating across different timelines and trying to prevent something in the past of the future protag from happening and achieving something in the future of the past protag.

This is a Chinese version of Kdrama "Signal". Plots are similar where the main characters who are police officers from different generations talk to each to solve cold cases.

Unknown Number is the chinese adaptation of the korean drama Signal. I wonder why noone subbed it yet.