How to convert plink data from 38th assembly to 37

My goal is to downgrade plink(.bed, bim, fam) data from the 38th build to 37. What is the easiest way to do this?

I was reading liftOver documentation and I am confused. Because it only accepts its own .bed format to do the lifting. It looks like I can prepare such a file, from plink bim, but what with the rest plink files, bed, and fam? Are they not require any modification? Also if I were to create a liftOver bed file, I notice that there are two coordinates for each SNP:

chr1    743267  743268  rs3115860
chr1    766408  766409  rs12124819
chr1    773885  773886  rs17160939

And there is only one coordinate in the plink .map file, how do I convert my map file?