If you're using BS4 sass, you can simply copy the code between the "pre" tags (below) into your variables file.
//This would go in your bootstrap variables file, overwriting the BS variables
$state-success-text: #fff !default;
$state-success-bg: #68C934 !default;
$state-success-border: darken($state-success-bg, 10%) !default;
$state-info-text: #fff !default;
$state-info-bg: #45ABCD !default;
$state-info-border: darken($state-info-bg, 10%) !default;
$state-warning-text: #fff !default;
$state-warning-bg: #ff9800 !default;
$state-warning-border: darken($state-warning-bg, 10%) !default;
$state-danger-text: #fff !default;
$state-danger-bg: #9E170E !default;
$state-danger-border: darken($state-danger-bg, 10%) !default;