I've created this tool: https://lingtalfi.com/bootstrap4-color-generator, you simply put primary in the first field, then choose your color, and click generate.
Then copy the generated scss or css code, and paste it in a file named my-colors.scss or my-colors.css (or whatever name you want).
Once you compile the scss into css, you can include that css file AFTER the bootstrap CSS and you'll be good to go.
The whole process takes about 10 seconds if you get the gist of it, provided that the my-colors.scss file is already created and included in your head tag.
Note: this tool can be used to override bootstrap's default colors (primary, secondary, danger, ...), but you can also create custom colors if you want (blue, green, ternary, ...).
Note2: this tool was made to work with bootstrap 4 (i.e. not any subsequent version for now).