First, please make sure that the offshore software development vendor understands your requirement and setup a right team based on your needs.
Secondly, talk to the team frequently to know their concern and pain points.
Third, if can't change the technology or make more challenges to motivate them, talk to their manager to find the replacement as soon as possible, and do the handover process properly.
You can read more about offshore development guideline here:
https://saigontechnology.com/blog/offshore-software-development-ultimate-guide