Another myth is that keywords in Google My Business influence rankings. Many people add a bunch of keywords to the description field, and their company description starts to look like "Miami plumbing company, emergency water repair, serving Miami and surrounding areas, water pumps, water heater repair, plumbers, commercial and residential plumbing services."
But the truth is, Google doesn't index this ranking field in any way, no matter how many keys you put in there. The best thing you can do with this field is to use it as a sales copy. Get those who see this field interested in your business, tell them what you do. Use this field for conversion purposes, not for ranking. You can see detailed instructions from Google on how best to use this field and how to use it to improve its ranking here.