Manually
To install this module copy the code from this repo to app/code/Space48/AdminPaymentMethod folder of your Magento 2 instance, then you need to run php bin/magento setup:upgrade
Via composer:
From the terminal execute que following:
composer config repositories.space48-adminpaymentmethod vcs git@github.com:Space48/AdminPaymentMethod.git
then
composer require "space48/adminpaymentmethod:{module-version}"