How do I backup my Apple Watch without my iPhone?

A month ago on Christmas Day, my iPhone that my Apple Watch was connected to was having issues with the homescreen and apps would kept crashing. When I restarted it the screen on the iPhone would stay at the Apple logo. It took me 2 weeks to get it back up and running and the only way was to format it. When my phone was back to life and brand new I noticed that my Watch series 4 wasn’t paired with my iPhone. I couldn’t use the activity app and view my medals or configure settings for the watch using my iPhone. On my watch I have loads of activity medals that I want remained period. I searched online to backup my Apple Watch but it says that you need your iPhone. I don’t have a watch backup on my phone and I really don’t want to delete my watch data and push myself to run 10km per day to get my activity medals back. Couldn’t I just back it up only using the I Mac and watch cable? Or I will format the watch and push myself to run 10km per day to get my activity medals back. Please find a way to do this with out a backup on the iphone. Many thanks.