Opencart, how to assign a buyer group to an unauthorized user?

Question

HTTP Cookies

Hello, is it possible to somehow assign a buyer group to an anonymous user, depending on the cookie of the city from which he comes? More:
There is a GEOIP plugin that writes the city cookie.
There is another plugin that allows you to show different prices to different user groups (screenshot)
It is necessary that with certain cookies prices for a certain client group are displayed. That is, some condition is needed, probably "IF cookie [city] == moscow THEN buyer group = central region" for example. And the plugin itself will slip the right price.
But I can not find information on how to redefine the group, maybe someone came across.
imgur.com/a/ydGoW
OpenCart 1.5.6